HK MR223 failure to feed in cold

[Near miss]

Hello,

I got HK MR223 as used 1 year ago and it had had over 2k through it, the surface of the gun was in very nice condition but the barrel looked it could have been more than 2k. Shortly after buying it I shot 200-400 rounds with it in 2 days in -17C/1.4F to -10C/14F without cleaning and no issues turned up.

I have used it with legacy type silencer with gas port turned to silencer mode for 3k-4k and maybe 500 with brake. I just got a flowthrough suppressor though.

Anyways, this winter it has started to give failures to feed, gas block set to nonsuppressed, without a silencer, the first 2-8 shots depending on how cold the gun is, between -20C/-4F to -8C/18F.
Once it is warmed up it will feed but the bolt might still not lock open after the mag runs out.
The brass goes in to a very small pile at direction of 15:30 once it gets going.

Could you please help me what could be the source of this problem?
Could it be that the legacy suppressor has slightly clogged the gas port? My firing has been steady except for few trainings with rapid fire but they were not long lasting. Maybe I should run it hot to get rid of any debris there?
Could it be any of the springs?

I have tried running it with normal grease, extra grease and now bone dry. The problem does not seem to change at all with lubes.

I am shooting 55gr Geco as my training ammo, I have not yet tried if 77gr Sellier loads produce the same problem. I have also tried PMC 55gr and it also had same issues.

I am open to more questions and of course, answers


EDIT 12/2023
In hindsight, this could be my HK gas block that created this. I had it stuck and had to turn it one day, (I used it quite often, really, but managed to shoot few K ammo inbetween) and when turning from S to N, it somehow failed. As a result it stuck to either side but wiggled a bit.

This summer (!!!!) I noticed I got few failure to feed at the range while prepping for a comp. I immediately assumed it was the gas block because I had read a much more of them over here. I used a magnet (lol) to hold the gas setting in place and rifle has ran very well through bushes and firing maybe 600-800 rounds so far (dry spell).

I hate that adjustable gas blocks can cause so much havoc. Should have known that it was fubar when it wiggled around. I tried fixing it myself but could not get the spring to apply pressure enough so I am guessing some metal piece broke off.

If I remember right, in the summer, I can run the rifle with Suppressed setting without the can.

But in the winter time, I think I had some problems with the low pressure cans as it is indeed is quite low pressure. The legacy can is ofc fine.
So, I am going to change to original (fixed) gas block and keep running the low pressure can.

 

[gimpy]

Have you tried any hotter ammo?

 

[Milf Dots]

Sliding parts- Use 100% synthetic LIGHT to very light grease for cold temps.
Pivoting/Rotating parts- use synthetic oil.

Try a brand new PMag m3 or Lancer L5 AWM mag if you haven't already tried different mags.

Inspect the barrel feed ramps for smoothness and cleanliness.

GECO is good ammo but that doesn't mean it isn't a defective/underloaded lot you have. PMC is notorious for being underpowered/low charged.

 

[Milf Dots]

And I'd clean the gas valve.

 

[TheGerman]

Try legit M193/855 and see.

If it still happens then you either have a gas leak somewhere, or you need a lighter spring/buffer just like the G3 does in cold weather as well as what lube do you use in such cold weather?

HK gave us different light blue coated springs and some cold weather lube after we had issues like this as well as the bolt sticking shut with the G3 when we were at freezing temperatures.

 

[Near miss]

Thanks for the replies!

Have you tried any hotter ammo?

I do have 55gr Sellier that is at least hotter than Geco and PMC, PMC is indeed very mild.

Sliding parts- Use 100% synthetic LIGHT to very light grease for cold temps.
Pivoting/Rotating parts- use synthetic oil.

Try a brand new PMag m3 or Lancer L5 AWM mag if you haven't already tried different mags.

Inspect the barrel feed ramps for smoothness and cleanliness.

GECO is good ammo but that doesn't mean it isn't a defective/underloaded lot you have. PMC is notorious for being underpowered/low charged.

I have used Light motor oil and Transmission fluid also. It has worked "before".

I am using multiple Pmag M3's but since the bolt does not lock open, I have not tried messing with other mags. I have one HK HR mag that is sprung well.

I have not checked the feed lips but ejected live ammo has no marks of any kind on them and I keep the area clean by sometimes spraying breakclean there. It is quite tidy.

I am going to try the Sellier 55gr.

And I'd clean the gas valve.

I will attempt to. I guess I will let some oil sit there and then at the range clean barrel of any possible oil and shoot the stuff off?

Try legit M193/855 and see.

If it still happens then you either have a gas leak somewhere, or you need a lighter spring/buffer just like the G3 does in cold weather as well as what lube do you use in such cold weather?

HK gave us different light blue coated springs and some cold weather lube after we had issues like this as well as the bolt sticking shut with the G3 when we were at freezing temperatures.

We have no legit M193 where I am but going to test hotter stuff. I am not sure how to determine gas leak, I can see that there is some carbon near the gas block, how should I check if it is causing the problem?

I have used light motor oil and ATF as lube. It has worked before (not just the shooting done 2 days after buying, but multiple other range visits last year at subzero)

I am thinking of buying another buffer for winter, mild/neutral 55gr loads and cold powder do not add up to good. But I also wonder how it has previously worked. Which spring strength would you recommend?

 

[TheGerman]

It sounds like its changing its gas 'state' from rounds 1-8 and then any rounds after its warm.

From the OP:

"Anyways, this winter it has started to give failures to feed, gas block set to nonsuppressed, without a silencer, the first 2-8 shots depending on how cold the gun is, between -20C/-4F to -8C/18F."

That's a sign of being undergassed.


"Once it is warmed up it will feed but the bolt might still not lock open after the mag runs out."

Thats a sign of being overgassed/bolt running too fast



"The brass goes in to a very small pile at direction of 15:30 once it gets going."

That's the correct position, but people put way too much weight into this.



Sounds like a mix of a few things.

The freeze point temperature of your lube is higher than you think it is (it freezes sooner). Clean literally 100% of the moving parts, then spray with isopropil and then apply a known ridiculously low freeze point lube. CherryBalmz makes one for cold weather if I remember right; or just switch the light oil you're using to just change that variable. Also, are you using too little/too much? Lube quantities usually don't matter as much until it gets super cold.

This could explain the shift from undergassed/slow bolt to all of a sudden overgassed/fast bolt within 10 shots as your molasses lube warms up.

The other variable to look at is getting a 'freezing cold setting' on your gun where you test and see what setting on the gun it needs to have plus what buffer and spring weight it needs to function 100% from round 1 to round 30.

If the gun is doing the 'wont hold open' dance once its warm, you're gun with the current gas settings is running the bolt fast/overgassed at baseline and just having 'cold' issues on the way there.

With this I'd also then mess with different buffer weights + spring. For a overgassed gun, heavier buffer + harder spring combat the issue, its a matter of figuring out what combination will give you function with the gun being both cold and hot. I'd get all 3 buffer weights, Sprinco springs that are Red/blue/white and then start testing.

This could be a combination of a different gas setting + buffer weight + spring to achieve your 'cold weather operating' setup.


This is a dance you find out at MWCS. Your weapons that worked all the time all of a sudden just randomly didn't anymore, and shit you thought didn't matter, all of a sudden does.

 

[Near miss]

I would guess the bolt hold open problem is more related to being undergassed. Not 100% sure but the recoil feels very mild to non-existent. To be fair, it has so far happened only once, after having already started shooting but it might be a pause caused it as the gun got colder again.

I am also quite confident that my current motor oil lube (5w-30) does an ok job, but not brilliant for sure.

I will buy a spring set for it and it should set it.

How about the gas block, should there be any carbon coming out of it? Since it seems to leak a tiny bit from the adjusting screw or somewhere around it. It was installed by the dealer when I bought it.

 

[TheGerman]

I would guess the bolt hold open problem is more related to being undergassed. Not 100% sure but the recoil feels very mild to non-existent. To be fair, it has so far happened only once, after having already started shooting but it might be a pause caused it as the gun got colder again.

I am also quite confident that my current motor oil lube (5w-30) does an ok job, but not brilliant for sure.

I will buy a spring set for it and it should set it.

How about the gas block, should there be any carbon coming out of it? Since it seems to leak a tiny bit from the adjusting screw or somewhere around it. It was installed by the dealer when I bought it.

The lube can be an issue in the extreme cold, I'd honestly find something for this to try.

Gas block wise, a bit of carbon around the block is normal. Since you have an overgassing state when its warmed up, I wouldn't think you have a leak thats causing issues.

 

[javemtr]

Can you specify what model MR223 you have? There are no MR223 coming from the factory with an adjustable gas block, so maybe this is an aftermarket part and could be source of your problems as others have already mentioned?

 

[Near miss]

Can you specify what model MR223 you have? There are no MR223 coming from the factory with an adjustable gas block, so maybe this is an aftermarket part and could be source of your problems as others have already mentioned?

It is A3 and indeed this one did not come with adjustable gas block, the dealer had them in stock so I grabbed one. Some A3 come with one from the factory I think.

 

[javemtr]

No, HK does not offer any civilian rifles with an adjustable gas block at this time! Can you tell us which gas block you had installed after purchasing the rifle? Maybe take a picture? I guess either it's a bastardized HK adjustable gas block (from the Norwegian contract or maybe an A5 block, although I have never seen a functional A5 gas block offered for sale anywhere) or a Waffen Burk gas block.
Are there any other modifications made to the rifle you failed to mention?

 

[Near miss]

I will try to record slow motion footage of the bolt moving the next time I am at the range, though the devices do not like cold so I am doubtful how it will go. There is some warm air coming soon for few days.

The gas block installed is this one:

Otherwise I have not messed with the rifle at all.

 

[javemtr]

Ok, so it is one of the Norwegian gas blocks. If no solution is found here, may I suggest you head over to the HKPro forum since your question is so HK specific. There are a number of folks over there that have messed with this gas block and may be able to help you.

 

[Milf Dots]

OP, keep the info coming as you learn more.

 

[Near miss]

Ok, so it is one of the Norwegian gas blocks. If no solution is found here, may I suggest you head over to the HKPro forum since your question is so HK specific. There are a number of folks over there that have messed with this gas block and may be able to help you.

Thanks for your help, everybody.

I will head over to HKpro (and you will get rid of me ) once I have tried
1a) hotter ammo (or really just standard rather than training ammo) While this will not solve my issue with my current stocked ammo, it will prove that the gun is not inherently broken, not the best thing but I also shot some Sellier last year, with PMC. Eventually PMC won with slightly better groups and far better price, the main factor.
1b) shooting the gas block hot with hotter ammo, in case the current slow shooting rate has produced extreme fouling, no d
2) footage that shows how the bolt acts (is it just small movement during the first shot, also when will the bolt start to hold open on last round?)
3) cleaning the gas block with boretech terminator or ballistol suppressor cleaning oil (it softens the caked on carbon)
4) weaker buffer spring. I would really like to have an all year round gun, but in local conditions it is hard to do without some serious overgassing in the hottest days, this years main competition was in 34C/93F. So I get it that to run smooth, 2 springs should be used. I am going to store this week anyways so I will grab few.
5) And lastly, as a back up, return back to original gas block. I really rather not do this.

No matter the suggestions I may get at HKpro, I will probably come around to same tests until further investigations / diagnoses are done. I am far from an expert or even knowledgeable but I suspect there are only so many parts that change cycling behavior by changing/degrading over time and that is the gas system and buffer spring, the masses/weights certainly have not changed.

My oil and oiling habits have kept to same but if changing that I could overcome this, it could be neat but I am so far a bit doubtful, my pistol (P10C) is quite well oiled too with the same oil and regime and it runs very well in the same conditions. Luckily it runs or otherwise the last competition would have been nothing but bottoms.. Good failure training, have not done that in such a fashion in a looong time!

 

[Near miss]

Yesterday was a nice weather to test this with my brother. Some things I remembered to check and some not. But I got little wiser and some hope too.

Test:
When racking the gun after being taken from the trunk the bolt moved very smoothly and without any extra effort, so I assume the lube is doing good. Temp was around -16 to -18C so around 0F.
I first took some slow motion footage of the feeding issue. The bolt moved maybe around a 3/5ths of the required distance with brake.
*I might have messed the below Sellier and Geco footage but likely not.*

Sellier with brake.mp4

MP4 File

1drv.ms

Geco with brake.mp4

MP4 File

1drv.ms

With flowthrough suppressor (meant to be used with gas block set to normal) it managed to misfeed a cartridge and pulling the charging handle caused a double feed. I had this happen to me with a break in night shooting competition last weekend.

Sellier with suppressor.mp4

MP4 File

1drv.ms

Here is a video of the gun chambering a round by pressing the bolt catch, for bolt movement reference:

Round chambered by releasing bolt.mp4

MP4 File

1drv.ms

Just to see what happens, we also tried the suppressed setting on the gas block while braked and it failed to eject at all.

Gas block set to suppressed.mp4

MP4 File

1drv.ms

We then continued to test how the rifle acts when it warms up.
After shooting around 1 and half mags, the ejection pattern changed dramatically.

Microsoft OneDrive

Also the shooter noticed the increased gas.
This is when we then tried to wait for the gun to warm up to continue firing it cold again but it took too long.

I returned to the range 2,5 hours later and shot one round of Sellier with flowthrough suppressor (it was freaking late, I figured 1 suppressed shot is not too bad) and it fed the next round right away. I cannot say if this was luck or not, but it did feed succesfully and it was not warm anymore for sure. This will be solved on the next range visit. I remain neutral so far.

Edit:
I just found the cartridge that was yesterday chambered in. It was a lucky feed, it obviously hit the feed ramp on its way. Still strange as hours before it did not get it chambered even it had been shot a few times. I now check the spring selection near me.

 

[MontanaMan]

Hello,

I got HK MR223 as used 1 year ago and it had had over 2k through it, the surface of the gun was in very nice condition but the barrel looked it could have been more than 2k. Shortly after buying it I shot 200-400 rounds with it in 2 days in -17C/1.4F to -10C/14F without cleaning and no issues turned up.

I have used it with legacy type silencer with gas port turned to silencer mode for 3k-4k and maybe 500 with brake. I just got a flowthrough suppressor though.

Anyways, this winter it has started to give failures to feed, gas block set to nonsuppressed, without a silencer, the first 2-8 shots depending on how cold the gun is, between -20C/-4F to -8C/18F.
Once it is warmed up it will feed but the bolt might still not lock open after the mag runs out.
The brass goes in to a very small pile at direction of 15:30 once it gets going.

Could you please help me what could be the source of this problem?
Could it be that the legacy suppressor has slightly clogged the gas port? My firing has been steady except for few trainings with rapid fire but they were not long lasting. Maybe I should run it hot to get rid of any debris there?
Could it be any of the springs?

I have tried running it with normal grease, extra grease and now bone dry. The problem does not seem to change at all with lubes.

I am shooting 55gr Geco as my training ammo, I have not yet tried if 77gr Sellier loads produce the same problem. I have also tried PMC 55gr and it also had same issues.

I am open to more questions and of course, answers

My comments are free so take them for what they are worth.

First, your gun is surely not over-gassed, either cold or warm, no matter what some may think. The combined facts that it doesn't pick up the next round from the mag & that it does not lock back on an empty mag clearly point to being under-gassed.

2nd, take the adjustable GB off & replace it with the OEM part.

3rd, thoroughly glean the bolt in all aspects & lube with a know low temp freeze point lube......this is very important if you want the gun to run cold from the 1st round fired.

4th, test the gun unsuppressed with the Geco & some other higher pressure ammo; there's no substitute for NATO pressure 77 gr ammo in low temps, 55 NATO if you can't get 77's.

If the guns functions reliably unsuppressed, then you can try suppressed as you see fit.

If all is well, at this point, buy another make of adjustable gas block.............IMHO, SLR is unsurpassed & can be easily cleaned w/o removing it.

Using a lighter buffer may be something you might want to test later.................my preference is always to use the lightest buffer & spring that will run well & not unlock too fast.

Good Luck.

MM

 

[javemtr]

If all is well, at this point, buy another make of adjustable gas block.............IMHO, SLR is unsurpassed & can be easily cleaned w/o removing it.

He's talking about a piston-driven HK MR223, so some random AR-15 direct impingement gas block is not gonna solve his issues. All your other recommendations are solid though

 

[killer-e]

Do they use a hydraulic buffer?
if so I would say that is your problem.

 

[Near miss]

Do they use a hydraulic buffer?
if so I would say that is your problem.

From what I have understood the buffer weight is filled with tungsten powder and the spring is quite regular wirespring

 

[GBMaryland]

I have to agree with other folks that it’s probably something related to the gas block / ammo combo.

With a piston upper you really shouldn’t have too much in the way of issues.

 

[Near miss]

I have to agree with other folks that it’s probably something related to the gas block / ammo combo.

With a piston upper you really shouldn’t have too much in the way of issues.

Indeed. Very strange. I will test Sellier 77gr sierra load next time.
Btw. While there is no major gas leak, is not gas block leak irrelevant since it has the vent hole in it anyways? Some carbon escapes from the point the gas block is switched between N/S.

Returning back to original block seems now more certain as I am very happy with the flowthrough suppressor. It is a bit more longer and heavier and is not as effective but it sure makes the gunshot sound very quiet without ear pro, I still use in ear CAEs ofc.

If required to change the spring, this should be good? It is the only spring offered by the nearest store, I can order some others from brownells.
JP RIFLES TUNED AND POLISHED BUFFER SPRING, .223 RIFLE

 

[Milf Dots]

I'd return the rifle to full OEM parts, then test fire without suppressor. Then test fire with suppressor.

Remember to only change one part, one variable, at a time. Change ammo, then test. Change spring, then test. Change gas block, then test.

 

[AngryKoala]

OP,

In terms of lubrication, what others are calling the "freeze point", you will see listed on PDS/TDS as pour point. Aim for 10 -15 deg C below the lowest expected temperature.

 

[Near miss]

OP,

In terms of lubrication, what others are calling the "freeze point", you will see listed on PDS/TDS as pour point. Aim for 10 -15 deg C below the lowest expected temperature.

Just checked that the oil I tested the rifle with is rated -50C so far beyond the current temperature.

 

[AngryKoala]

Just checked that the oil I tested the rifle with is rated -50C so far beyond the current temperature.

Then it should be fine if not oxidized/contaminated. To have that kind of rating I'm assuming this was a PAO based fluid.

 

[MontanaMan]

He's talking about a piston-driven HK MR223, so some random AR-15 direct impingement gas block is not gonna solve his issues. All your other recommendations are solid though

Ahhh, yes...................wasn't paying full attention. Thanks.

MM

 

[Enbloc]

sounds like a gas issue. Te colder you are, the lower the port pressure. Low port pressure means low cyclic speed and can induce failures to feed, and failures to lock back on an empty mag.
Hk mr223s are slightly less gassy than the military 416, so with low power ammo you can run into low pressure issues in cold weather. The same thing happens to other high end rifles as well.
try shooting 556 pressure ammo, all the ammo you listed are particularly underpowered, even for 223 specs. Try some mil spec m855, or better yet mk262 mod 1 or mk 318

 

[Near miss]

sounds like a gas issue. Te colder you are, the lower the port pressure. Low port pressure means low cyclic speed and can induce failures to feed, and failures to lock back on an empty mag.
Hk mr223s are slightly less gassy than the military 416, so with low power ammo you can run into low pressure issues in cold weather. The same thing happens to other high end rifles as well.
try shooting 556 pressure ammo, all the ammo you listed are particularly underpowered, even for 223 specs. Try some mil spec m855, or better yet mk262 mod 1 or mk 318

I will try to find some good ammo, I have some loose boxes stored, at least few 62gr from magtech.
The weather has been very mild now so I have not been able to test further. Maybe a week or so to wait.

You guys are right, the ammo is most likely the culprit here since it really is different from standard. But I guess to mitigate the effect from ammo the buffer spring is probably the ideal part to change? I get the PMC and Geco 36 to 38 cents a piece with VAT and I have already quite lots of them I'd really like to keep shooting them.

 

[Enbloc]

you could use slightly lighter buffer or spring. What spring/buffer weight are you using?

 

[Near miss]

you could use slightly lighter buffer or spring. What spring/buffer weight are you using?

Original ones. Or at least should be the original ones. The buffer has red paint on it but the spring does not. I am aware that they have varied that policy, so could be or could be not. At least by the strength of it, seems original too.

I went to nearest gun store today and they had JP rifle spring there, I took that. I thought of testing the weight needed to pull the charging handle before going to range. It is getting colder again next week.

Even if it is the ammo I think it is still strange that after few manually cycled shots it starts cycling. And the cycling also changed while emptying the second mag. Nothing in the action really warms up by then to cause a change so I do not know where something is switched.

 

[RUTGERS95]

break rifle down and clean thoroughly
clean and check gas block, possibly remove and inspect but as mentioned before, pressure drops with temp
use light layer of mobil 1 (few drops on your finger and rub (I have done this is below freezing temps in Alaska with zero issue) light application
standard ammo should work
measure gas port as well

 

[RUTGERS95]

Original ones. Or at least should be the original ones. The buffer has red paint on it but the spring does not. I am aware that they have varied that policy, so could be or could be not. At least by the strength of it, seems original too.

I went to nearest gun store today and they had JP rifle spring there, I took that. I thought of testing the weight needed to pull the charging handle before going to range. It is getting colder again next week.

Even if it is the ammo I think it is still strange that after few manually cycled shots it starts cycling. And the cycling also changed while emptying the second mag. Nothing in the action really warms up by then to cause a change so I do not know where something is switched.

agree, wonder if the carrier is riding? then again, it has 2k+ rounds on it so the receiver should be 'worn' to that.
I'm betting gas block/port

 

[Evintos]

Judging from your slowmo video. You're under gassed due to the temps and low port pressure of the ammo you're shooting. Short cycling is happening, your round is ejecting to the 4-6 o'clock (16:00-18:00H position. The more rounds you shoot, the warmer the barrel will get and the tiny bit of heat helps it to function normally again (your barrel will be warmer than the BCG, receiver, and handguard; measure the temperature at your gas block and you'll find many degrees different) and you start seeing normal function with the ejection port shifting to the 3 o'clock (15:00h) and when it gets excessively hot it'll be closer to 13:00H.

Some things you can do if you want to continue to shoot the ammo you have.

1. Keep that ammo warm (under your jacket close to your body). Don't use direct heat, but just keep that ammo above ambient air temps. You can leave the rifle cold.
2. Change the buffer out to a lighter buffer (416/MR556 buffer with the red dot is around 5oz or 142g). Go to a H2 equivalent (4.7oz or 133g). If you're super frugal - knock out the pin in your buffer and pour some of the tungsten powder out until you reach about 4.7oz or 133g (weight includes the pin, bumper, and buffer body). Make save the powder so you can pour it back in during warmer weather. You can keep the original spring in there, those things are good for like 10k+ rounds.

You should however just purchase a lighter buffer (rather than modifying your current buffer) and then switch out to the 416/MR556 standard buffer during warmer temps. Not sure how much they cost in Finland. After changing the buffer weight you may still have to keep the gas block in normal mode even while shooting supressed.

If you want to use motor oil as a lube, at the winter temps found in Finland, consider switching to 0W viscosity oil.

 

[Near miss]

Judging from your slowmo video. You're under gassed due to the temps and low port pressure of the ammo you're shooting. Short cycling is happening, your round is ejecting to the 4-6 o'clock (16:00-18:00H position. The more rounds you shoot, the warmer the barrel will get and the tiny bit of heat helps it to function normally again (your barrel will be warmer than the BCG, receiver, and handguard; measure the temperature at your gas block and you'll find many degrees different) and you start seeing normal function with the ejection port shifting to the 3 o'clock (15:00h) and when it gets excessively hot it'll be closer to 13:00H.

Some things you can do if you want to continue to shoot the ammo you have.

1. Keep that ammo warm (under your jacket close to your body). Don't use direct heat, but just keep that ammo above ambient air temps.
2. Change the buffer out to a lighter buffer (416/MR556 buffer with the red dot is around 5oz or 142g). Go to an H2 equivalent (4.7oz or 133g). If you're super frugal - knock out the pin in your buffer and pour some of the tungsten powder out until you reach about 4.7oz or 133g (weight includes the pin bumper and buffer body). Make save the powder so you can pour it back in during warmer weather. You can keep the original spring in there, those things are good for like 10k+ rounds.

You should however just purchase a lighter buffer (rather than modifying your current buffer) and then switch out to the 416/MR556 standard buffer during warmer temps. Not sure how much they cost in Finland. After changing the buffer weight you may still have to keep the gas block in normal mode even while shooting supressed.

Thanks. Can you brief me what is the interaction between buffer and buffer spring?
Weight or spring power, why choose one over the other?

They do not cost much but selection is not very wide in a single shop.

I just tested the buffer spring with a string attaching charging handle to a backbag that acted as a weight. I lowered the backbag slowly and checked where it ends. The JP spring seems to be maybe a slight touch lighter but it is practically the same, the error margin is almost equivalent but carefully tested, this should be close to truth. Of course, that small distance might be just what is required.

I linked some photos to this post, showing the difference in bolt movement, springs compared and the carrier damage to receiver, the photo may not show it but the wear there is very cosmetic and I kept an eye on it at the beginning but it really does not change at all.

 

[Evintos]

At the gas port, the gas pressure (which is energy) gets siphoned into the gas block which pushes onto the piston and then moves the operating rod (these also have mass), which then impacts the anvil face aka "tombstone" of your bolt carrier pushing the carrier back (your bolt unlocks by rotating, the timing of which is dictated by the cam track) and the bolt carrier pushes onto the buffer, some of this momentum is absorbed as the spring compresses and the potential energy stored in a compressed spring acts in reverse in the system - pushing everything forward. There is a minimum amount of energy input in order to start this chain of events and that's from combusted gasses from the fired round.

Edited to add - when the moving mass still retains enough energy to continue traveling rearward but cannot physically, the energy is then transferred into your body (effects of recoil). Also forgot to add the that the op rod spring returns the op rod and piston back into position ready for the next burst of gas energy.

Your buffer is part of the overall mass that has to move in order for your action to cycle whereas the spring absorbs and converts some of the momentum of the moving mass into stored energy. The spring being the object that has to have enough energy/force to push the reciprocating mass (buffer and bcg) as well as the ammunition (because ammo has mass as well) forward into battery (loading a round). The spring can be so weak that it does not have enough force to push the buffer and bolt carrier group forward with enough energy to strip a round from the magazine and shove it into the chamber all while having to overcoming friction.

Changing the mass is easier than trying to change springs because the way a spring acts while it's being compressed. The measurement of spring force/strength isn't linear. The rating of spring strength is usually at maximum compression. Mass however is static. It weighs what it weighs. Heavier mass requires more energy to accelerate, lighter mass = less energy. Imagine yourself pushing a sedan on wheels vs pushing an armored vehicle on wheels, which one requires more force to even begin to move. The combusted gasses from your temperature sensitive ammo in the cold is producing very low gas pressure (in this case measured at the gas port rather than chamber, although that's also low with the temps). Lower temperatures = lower air pressure = less energy, higher temperatures = higher air pressures = higher energy. The residual heat from the previously fired rounds is increasing the temperature inside the bore of your barrel, thus in the cold, the more you shoot, the faster it returns to normal functions.

The fixes are either introduce more energy into the system via higher pressure ammo, higher temperature, or modify (drill) the adjustable gas port rotating drum to have larger ports, or lower the energy requirement to move everything (going to lighter buffer).

If you drill the holes in your AGB to let more gas flow for the winter, just note that in summer time when temps are higher, your adjustable gas block is now letting more gas pressure push onto the mass in the system and it will leave you over gassed.

Buffer change is cheaper, faster, less expensive (compared to figuring out optimal spring return strength). For the two position adjustable gas block, 1 winter buffer weight (H1 or H2 equivalent) and 1 spring/summer/autumn weight will work for you year round, both suppressed and unsuppressed. By lowering the spring strength, sure the system will end up requiring less force to compress the spring, but it also means it'll have less force/energy/strength to push everything back forward. You will potentially have feed related issues even in the summer due to the excessively weak spring.

For the HK416/MR556/MR223 - usually the standard (red dot buffer which is around 5oz) and a slightly lighter one will more than likely fit your needs, just switch out as the temps change.

If you want to shoot with even lower pressure ammunition such as subsonic ammunition in the cold, you'll want to even go as far as H1 weight (3.8oz or 107grams) and maybe even lower to 3oz or 85grams.

Ultimately it's up to you what you want to do, but the lighter buffer allows you to continue to shoot the ammo you have at freezing temperatures without having to worry about feed related issues caused by a weaker spring.

As for the wear marks on the bottom portion of your receiver extension (aka buffer tube), that is normal and characteristic of a phenomenon called "carrier tilt" which is inherent to short stroke gas piston designs integrated into an M16/M4/AR15 form factor. Design of the bolt carrier at the tail will limit the amount of tilt however tolerance stack between parts will inevitably result in some wear. If it really bothers you, you can switch to a receiver extension with an extended lip (ex. PWS enhanced buffer tube).

 

[Near miss]

At the gas port, the gas pressure (which is energy) gets siphoned into the gas block which pushes onto the piston and then moves the operating rod (these also have mass), which then impacts the anvil face aka "tombstone" of your bolt carrier pushing the carrier back (your bolt unlocks by rotating, the timing of which is dictated by the cam track) and the bolt carrier pushes onto the buffer, some of this momentum is absorbed as the spring compresses and the potential energy stored in a compressed spring acts in reverse in the system - pushing everything forward. There is a minimum amount of energy input in order to start this chain of events and that's from combusted gasses from the fired round.

Edited to add - when the moving mass still retains enough energy to continue traveling rearward but cannot physically, the energy is then transferred into your body (effects of recoil). Also forgot to add the that the op rod spring returns the op rod and piston back into position ready for the next burst of gas energy.

Your buffer is part of the overall mass that has to move in order for your action to cycle whereas the spring absorbs and converts some of the momentum of the moving mass into stored energy. The spring being the object that has to have enough energy/force to push the reciprocating mass (buffer and bcg) as well as the ammunition (because ammo has mass as well) forward into battery (loading a round). The spring can be so weak that it does not have enough force to push the buffer and bolt carrier group forward with enough energy to strip a round from the magazine and shove it into the chamber all while having to overcoming friction.

Changing the mass is easier than trying to change springs because the way a spring acts while it's being compressed. The measurement of spring force/strength isn't linear. The rating of spring strength is usually at maximum compression. Mass however is static. It weighs what it weighs. Heavier mass requires more energy to accelerate, lighter mass = less energy. Imagine yourself pushing a sedan on wheels vs pushing an armored vehicle on wheels, which one requires more force to even begin to move. The combusted gasses from your temperature sensitive ammo in the cold is producing very low gas pressure (in this case measured at the gas port rather than chamber, although that's also low with the temps). Lower temperatures = lower air pressure = less energy, higher temperatures = higher air pressures = higher energy. The residual heat from the previously fired rounds is increasing the temperature inside the bore of your barrel, thus in the cold, the more you shoot, the faster it returns to normal functions.

The fixes are either introduce more energy into the system via higher pressure ammo, higher temperature, or modify (drill) the adjustable gas port rotating drum to have larger ports, or lower the energy requirement to move everything (going to lighter buffer).

If you drill the holes in your AGB to let more gas flow for the winter, just note that in summer time when temps are higher, your adjustable gas block is now letting more gas pressure push onto the mass in the system and it will leave you over gassed.

Buffer change is cheaper, faster, less expensive (compared to figuring out optimal spring return strength). For the two position adjustable gas block, 1 winter buffer weight (H1 or H2 equivalent) and 1 spring/summer/autumn weight will work for you year round, both suppressed and unsuppressed. By lowering the spring strength, sure the system will end up requiring less force to compress the spring, but it also means it'll have less force/energy/strength to push everything back forward. You will potentially have feed related issues even in the summer due to the excessively weak spring.

For the HK416/MR556/MR223 - usually the standard (red dot buffer which is around 5oz) and a slightly lighter one will more than likely fit your needs, just switch out as the temps change.

If you want to shoot with even lower pressure ammunition such as subsonic ammunition in the cold, you'll want to even go as far as H1 weight (3.8oz or 107grams) and maybe even lower to 3oz or 85grams.

Ultimately it's up to you what you want to do, but the lighter buffer allows you to continue to shoot the ammo you have at freezing temperatures without having to worry about feed related issues caused by a weaker spring.

As for the wear marks on the bottom portion of your receiver extension (aka buffer tube), that is normal and characteristic of a phenomenon called "carrier tilt" which is inherent to short stroke gas piston designs integrated into an M16/M4/AR15 form factor. Design of the bolt carrier at the tail will limit the amount of tilt however tolerance stack between parts will inevitably result in some wear. If it really bothers you, you can switch to a receiver extension with an extended lip (ex. PWS enhanced buffer tube).

Thanks for the clear explanation. I knew that it is essential that the spring must have enough energy to return the bolt forward. Explaining how the buffer weights differ in terms of capability per weight helped to put the system into perspective.
Not necessary but how would you go about if this needed to be a fixed setup, working all season? It seems that a strong spring with less weight would be the ideal to more weight, why is the heavier buffer used, smoothness?

I will buy a H2 buffer.
Have to say, the pressure changes tremendously in cold, comparing the previous video to how I can shoot breaked with few short strokes with the suppressor setting on when it is around 20C / 70F.

I do not mind the buffer tube wear, it will really take a long while to become a problem at this rate. It seems that after taking the sharpest corner off the bolt carrier now slides over it as the bcg is rounded at the back.

 

[Evintos]

The heavier buffer is used to delay the unlock time of the system. Ideally you want to keep the bolt locked into battery for as long as possible until the gas pressures in the bore drop to "safer" and more ideal levels. This reduces the wear and tear (strain) on various parts of the system particularly the cam pin, bolt lugs and extractor, as well as reduces blowback fouling coming from the chamber. This is based on a fixed gas port size that cannot be reduced via an adjustable gas block. Adjustable gas blocks delay unlock time simply by slowing down or stopping excess gas from initiating the cycling sequence.

1. For a single setup, all season "duty use," "I don't want to mess around with switching things out," "my life depends on this", the general solution is to be over gassed. Hence why a lot of law enforcement and military rifles are over gassed on purpose. This would mean rain, snow, ice, dirt, mud, sand, and high pressure or low pressure ammo will not affect function. Sticking with the H2 (maybe even H1) buffer year round, suppressed or unsuppressed will most likely get you there. The downside is you'll get harsher felt recoil in most conditions, and have faster parts wear (instead of say 20,000 rounds parts service life, potentially 15,000rds or less - never know due to manufacturing and other variables). Preventative maintenance (regular parts change intervals) will prevent you from having a "Oh shit, my gun broke" at critical moments.

2. The tuner solution (comes from the competition side of the shooting sports) uses normal strength (or even reduced strength) spring with lighter buffer to reduce the felt recoil from the reciprocating mass of the system. If you lock the bolt to the rear and hit the bolt release, you know that forward dip you get when the bolt slams forward? That gets reduced with low mass and a lighter spring. The lighter spring doesn't push the mass forward as hard, the lower mass reduces the impact force (getting hit by a brick vs getting hit by a feather). Force = Mass (buffer, bcg) X Acceleration (spring)

The combination of low mass bolt carriers, lighter buffers, titanium firing pins, etc. gives this result but ONLY, and this is critical, if there is an adjustable gas block. The adjustable gas block regulates how much energy goes into the system and you can control it so that only the minimum amount of energy required goes through for function based off conditions (ammo, temperature, suppressed/unsupressed).

***The closest tuner setup that'll you'll be able to achieve for the 416/MR556/MR223 at the moment (that I am aware of) is the Waffen Burk 5 position AGB. The more positions the better for tuning setups.

The positions are N+ (adversed, most gas), N (normal), S (Suppressed), 1 (suppressed 1), 2 (suppressed 2 least amount of gas). This gas block only works if the gas port of your barrel is larger than any of the gas ports on these settings. If it isn't, you have to drill or get a gunsmith to drill the gas port on the barrel so that it is equal to or larger than the largest port size in the AGB.

Afterwards, you want to select the buffer weight that results in best function (ejection 15:30 to 16:30) with setting #2 in summer on the hottest day with ideally the highest pressure ammo you can find and with your highest backpressure suppressor. Then as conditions changes and you need more gas, simply switch to the higher gas settings (1, S, N, or N+).

 

[Near miss]

Thank you again! The rifle is quite smooth during the summer too so I started thinking if I could have it all solved at once by permanently taking some tungsten powder from the buffer and still be on the comfortable side.

And then see in the summer if it is too much. I only have a scale up to 770gr/50g so I cannot weigh the whole buffer, I will measure maybe 154gr / 10g worth of powder to a minigrip bag. I guess it should be quite near to a H2 then.

Having used AKs I like the idea how they can serve all year around, although I do not see any a huge problem changing the buffer. If the recoil becomes too strong or the modified buffer does not help, I will buy the second buffer.

 

[Evintos]

Thank you again! The rifle is quite smooth during the summer too so I started thinking if I could have it all solved at once by permanently taking some tungsten powder from the buffer and still be on the comfortable side.

And then see in the summer if it is too much. I only have a scale up to 770gr/50g so I cannot weigh the whole buffer, I will measure maybe 154gr / 10g worth of powder to a minigrip bag. I guess it should be quite near to a H2 then.

Good plan. By modifying the current buffer, you have a lot of freedom to test weights. Starting off with the 10g removal is good and if you want to experiment further, you can always add back 2 grams at a time (or even remove 2g powder at a time). The most optimal weight (balance between reliability and felt recoil) that works year round could even end up between 142g (red dot buffer weight equivalent) and 133g (H2 weight equivalent) or a couple grams below H2.

Good luck!

 

[MontanaMan]

While adjusting buffer weights certainly has merits, dealing with 2 gram increments is rather laughable.

There's more variation in a single lot of most ammo than what the difference that 2 grams will make.

MM

 

[Evintos]

Unfortunately there's no infinitely adjustable gas block equivalent or multi-click (15+ settings) adjustable gas block equivalent for the 416/MR556/MR223 like the ones you can find on DI AR15's.

2 gram changes is equivalent to a 0.07oz change (3 grams = 0.105oz) which gives him basically 4 more available tuning "settings."

In another perspective - 2 grams = 30.86 grains. <- think of this in powder terms. Dealing with ~0.1 grains which is 0.0064 grams is a norm for handloaders.

Sounds ridiculous, but when you look at the weight differences between buffers, H1 3.8oz, H2 - 4.6-4.7oz, H3 5.4oz, there's only 22 grams roughly of difference between them, (less for a HK red buffer (5oz) to H2 - only 9 grams difference), 2 gram increments makes sense (if anything, if you want to fine tune, 0.1 grams which is 1.54 grains increments make even more sense.)

But again, it's a fine tune experiment if he wishes to partake in.

 

[MontanaMan]

I know the math well.

And, no disrespect intended, I'll stick with my comment about ammo variation within most lots as being more than enough to mask 2 grams difference in buffer weight.

And also, you simply cannot equate fine tuning a buffer system to the control of fine tuning a gas (via an AGB).................that's simply not apples to apples.

YMMV & obviously appears to, so carry on with the buffer fine tuning in 2 gram increments.

MM

 

[Near miss]

If 10g is enough to make a big difference, I guess 2g is enough make a small.

I think there is misunderstanding, indeed powder amounts vary a lot but the 10g is now the base and I will then add or take around 2g until it looks good. I mean, I might aswell take another 2g on top of that 10g. It should be better than to take another 10g off if the problem remains (unless the -10g does NOTHING). I do want the gun to run reliably, then smooth.

I hope I will get a drift of how the weight works after seeing the function with the lighter buffer.

I do not know what I do when the temperature drops down to -30C / -22, maybe become pacifist? I do not know how the pressure curve goes from -18 to -30 but I have noted and taught that the velocity drop with factory powders is very steep when it goes to freezing.

Well, we'll see.

I start to understand why every reloader does winter and summer loads here..

 

[Isaiah's Blacksmith]

What did the Marines do with their weapons at Chosin to get them to fire? They didn't have winter and summer loads.

 

[Evintos]

They shot the mighty full powered 30-06, ditched the 30 carbine when they could (this one we can only speculate why 30 carbine was ineffective yet 45acp was praised), mortared/kick started their frozen M1 Garands, BARs, fired their weapons periodically to keep them warm, piss on them, lots of malfunction clearing, so on and so forth. The cold does weird things to firearms.

Short answer - they did whatever it took because lives depended on it.

 

[Near miss]

Indeed. I too have had to mortar an AK, pretty much every conscript over here has some kind of experience with that, since the tents are very moist places, few nights or even worse, multiple short visits and you are set.

The firearms freeze tests are usually done on empty weapons, I think that most likely a loaded firearm would be a bit easier to get to function since once you fire the gas system works the gun the natural way quite efficiently, probably the first is misfeed but it is a lot easier to press a trigger and let the powder do its work than it is to mortar the gun. I have thought of testing this myself but I usually spend the nights under tarp on overnight shooting trips so I have never had those problems, I do not even go to shoot near the sea.

 

[RUTGERS95]

kerosene in the lube does wonders. My grandfather said he did this in korea as it's the coldest he's ever been. He also said in ww2 he never had cold related issues with his Garand but Korea was different. much of this happens when you go in and out from warm to cold. If you leave out and don't go back and forth before setting down for night, you didn't/don't have issues.

 

[bill alexander]

The gas port should measure 1.5mm diameter, the gas vent should also measure 1.5mm diameter. The set up is identical between the MR556 and the HK416 with a 16.5" barrel. Difference between the two is the heat treatment of the barrel and whether the barrel is chrome lined.

The adjustable Norwegian gas block is not set up for the MR556. Normally an adjustable block is not required if the rifle is tuned correctly.

Running M855 ammunition we test these rifles down to -65 Centigrade without problems when the correct artic lubricant is applied. All standard lube must be carefully removed and the firing pin channel is best left dry.