Buffer trouble.

[PNW_Steve]

Hey Everyone,

I am having some trouble sorting out correct buffer spring and weight.

Can anyone point me to a good troubleshooting thread or resource?

I have a 10.5, pistol gas, 300BO. I started with a carbine buffer and spring and had short stroking trouble. At the advice of a LGS, I replaced the carbine buffer with an H3. It still short strokes. Brass ejects but it doesn't pick up another round.

I also have an 18 inch, rifle gas, .223 Wylde that had the same problem.

What do you all recommend?

Thanks

 

[Bevo]

Who installed the gas block? Is it adjustable?

 

[USK308]

+1 on is gas block adjustable. My 10.5" 300BO SBR works like a champ with an H2 buffer (albeit a JP SCS H2 buffer spring).

Sounds like you are not getting enough has to push the BCG back fully for proper cycling.

 

[WeR0206]

Hey Everyone,

I am having some trouble sorting out correct buffer spring and weight.

Can anyone point me to a good troubleshooting thread or resource?

I have a 10.5, pistol gas, 300BO. I started with a carbine buffer and spring and had short stroking trouble. At the advice of a LGS, I replaced the carbine buffer with an H3. It still short strokes. Brass ejects but it doesn't pick up another round.

I also have an 18 inch, rifle gas, .223 Wylde that had the same problem.

What do you all recommend?

Thanks

Which type of short stroking did you see with carbine buffer & spring vs h3 buffer with same spring?

• Ejection ok for both but failure to lock back for both?
• failure to eject and lock back for both?
• or did one eject ok and the other didn’t?

This will provide needed context to help us troubleshoot.

Also do you happen to know how big the gas port hole in the barrel is?

I’m not too familiar with pistol length gas 10.5 inch 300 BO barrels. Do you happen to know how many inches of dwelltime there are (measure the distance between the gas porthole to the end of the barrel)? This will also provide needed context. In general, if you have a lot of dwell time, it’ll create an over gas type situation (higher operating pressure), but it all depends on the size of the gas port hole. If you have shorter dwelltime, then it’ll be a softer shooting rifle in general and will have lower operating pressure. These are generalizations and most good barrel manufacturers will optimize the size of the gas port based on how much dwelltime is in the barrel so that there is enough pressure to cycle the gun, but not too much.

One thing I would do asap is take out the bolt carrier and make sure the gas key screws aren’t loose (test @ 30 in-lbs with wheeler torque wrench etc). I had a short stroke issue that came out of nowhere with familiar ammo and it was bc one of the carriers gas key screws was sheared (the staking was keeping it in place though).

You could also try different combos of H1 and H2 buffers and different power springs (sprinco blue, white, red, etc) to see if you get the issue resolved. KAK industries sells a pretty cheap buffer tuning kit that has extra steel and tungsten buffer weights and is handy for tuning AR’s.

Although it’s frequently the cause Short stroking isn’t always caused by an under gassed gun, it could also be from too much gas (bolt goes too fast to pick up next round from mag based on mag spring tension).

For troubleshooting Here are a few resources for you to check out:

How to Fix Your AR 15 When It's Not Cycling

Few scenarios suck more than the following: you pull out your AR-15, load in a fresh magazine, drop the bolt, pull the trigger to fire one round, and then … nothing. Your

www.silencercentral.com

AR15BARRELS.COM - Randall's description of AR gas operation and how everything works in harmony

How the AR-15 gas system works

www.ar15barrels.com

 

[PNW_Steve]

on the .223 rifle:

With PMC 62gr it ejects the case but will not lock back. With Winchester Practice 55gr it fails to eject.

Gas port to muzzle measures 5 inches.

I don't know the gas port size. Here is the barrel: https://www.bsfbarrels.com/product-page/223-wylde


On the 300 BO:

Hornady Black 208gr ejects but does not lock back.

Gas port to muzzle is almost 6 inches.

Don't know the gas port size on this one either.

What else can I tell you?

 

[USK308]

on the .223 rifle:

With PMC 62gr it ejects the case but will not lock back. With Winchester Practice 55gr it fails to eject.

Gas port to muzzle measures 5 inches.

I don't know the gas port size. Here is the barrel: https://www.bsfbarrels.com/product-page/223-wylde


On the 300 BO:

Hornady Black 208gr ejects but does not lock back.

Gas port to muzzle is almost 6 inches.

Don't know the gas port size on this one either.

What else can I tell you?

FWIW, my 10.5" 300BO will NOT play nice with the Hornady 208 A-Max nor the 190 Sub-X. Mine runs flawlessly with S&B 200gr subs.

Mine has a Rosco Mfg 10.5" barrel with a Sup Arms AGB. I run mine @ 19 clicks open and it runs like a rock star.

 

[PNW_Steve]

Who installed the gas block? Is it adjustable?

I installed the one in the 223 and the 300BO was factory installed .

Barrel is dimpled. I torqued to 22 inch pounds.

 

[WeR0206]

on the .223 rifle:

With PMC 62gr it ejects the case but will not lock back. With Winchester Practice 55gr it fails to eject.

Gas port to muzzle measures 5 inches.

I don't know the gas port size. Here is the barrel: https://www.bsfbarrels.com/product-page/223-wylde


On the 300 BO:

Hornady Black 208gr ejects but does not lock back.

Gas port to muzzle is almost 6 inches.

Don't know the gas port size on this one either.

What else can I tell you?

Im not familiar with BSF barrels and they didn’t list the gas port size on the website which is odd. I would just call them and ask for your length 223 wylde what type of buffer weight/spring they recommend. I would also ask them the size of the gas port hole.

Re: the 300 BO you said you tested it (im assuming with the same ammo and same mil-spec spring) with carbine buffer weight and also with H3.

With carbine buffer did it fail to lock and feed?

With H3 buffer did it fail to lock and feed?

Once you answer those 2 questions we can try and direct you. I also mentioned checking the gas key screws in your bolt carrier. It’s also worth checking gas block screws.

 

[PNW_Steve]

Im not familiar with BSF barrels and they didn’t list the gas port size on the website which is odd. I would just call them and ask for your length 223 wylde what type of buffer weight/spring they recommend. I would also ask them the size of the gas port hole.

Re: the 300 BO you said you tested it (im assuming with the same ammo and same mil-spec spring) with carbine buffer weight and also with H3.

With carbine buffer did it fail to lock and feed?

With H3 buffer did it fail to lock and feed?

Once you answer those 2 questions we can try and direct you. I also mentioned checking the gas key screws in your bolt carrier. It’s also worth checking gas block screws.

Yes to both

 

[fedupflyer]

I assume you are running the 300 BO un-suppresed with subs. If that is the case a standard spring with an H2 buffer should work.
If you are running supers un-suppressed then a H3 is probably what you need.

For the 300 BO, I highly suggest using using 300 BO specific mags or aluminum GI mags. If you don't you will probably have feeding issues. Been done this road more than once.

 

[PNW_Steve]

I assume you are running the 300 BO un-suppresed with subs. If that is the case a standard spring with an H2 buffer should work.
If you are running supers un-suppressed then a H3 is probably what you need.

For the 300 BO, I highly suggest using using 300 BO specific mags or aluminum GI mags. If you don't you will probably have feeding issues. Been done this road more than once.

Yes, subs with suppressor.

Mags are Pmag 556. I will try aluminum mags.

I have a carbine buffer and an H3 buffer. If I swap one of the tungsten weights in the H3 for a steel weight, would that be equivalent to an H2?

 

[USK308]

Yes, subs with suppressor.

Mags are Pmag 556. I will try aluminum mags.

I have a carbine buffer and an H3 buffer. If I swap one of the tungsten weights in the H3 for a steel weight, would that be equivalent to an H2?

In answer to swapping tungsten for steel, yes, that would make it an H2.

 

[cas6969]

What else can I tell you?

Is this a SBR carbine, or a pistol, or a "pistol".
What length receiver extension?

 

[hlee]

Do either of these have adjustable gas blocks?

On a related tangent. It might be worth pulling the gas blocks to inspect for gas leakage.

 

[AznTactical]

I had similar issues on my 10.5" BO. Bolt was moving to fast before the next round could be pushed up in the mag. Went to heavier JP H2 captured spring and fixed this problem. This AR is tuned to be 100% suppressed.
Then found out the combination of tolerances between bolt catch, mag catch, upper receiver, lower receiver and Lancer magazines were not compatible. It would refuse to lock back on last round. I wanted to use Lancers on my blackout and leave the Magpuls for the 223/556. However this particular build I had to use Magpuls and problem with lock bolt back on last round went away.
I have zero issues with my Lancers on my other 2 Blackouts.

 

[TonyAngel]

Hey Everyone,

I am having some trouble sorting out correct buffer spring and weight.

Can anyone point me to a good troubleshooting thread or resource?

I have a 10.5, pistol gas, 300BO. I started with a carbine buffer and spring and had short stroking trouble. At the advice of a LGS, I replaced the carbine buffer with an H3. It still short strokes. Brass ejects but it doesn't pick up another round.

I also have an 18 inch, rifle gas, .223 Wylde that had the same problem.

What do you all recommend?

Thanks

First of all, if your lgs suggested a heavier buffer to fix a short stroking issue, I'd stop asking them for advise.

I'm gonna guess that this is something that you threw together. The problem could be any number of things. Leaking gas key, bad rings, really bad fit between the barrel and gas block, undersized gas port in the barrel, etc.

First, you need to be using dedicated 300bo mags with subs. They are much longer than supers and will get hung up in a 5.56 pmag or similar mags. Get yourself a proper mag and load one round into it. Chamber the round and fire it. Do this a few times. What happens? Does the bolt lock back on all of them, some of them, none of them? If it doesn't lock back on all of them, my guess would be that you're undergassed. Check gas port size. What size you should have kind of depends on whether you're running supers or subs ... suppressed or unsuppressed. Are you running a traditional can or flow through?

Despite what has become a popular notion, ARs are not just tinker toys. Just because your throw AR parts together and it comes out looking like an AR doesn't mean it's gonna run like it's supposed to and just asking what buffer and spring should I get usually doesn't lead to a solution.

I'm not ranting. I'm just trying to make the point that if you have a true interest, read a book. It will explain what all of the parts do and why. Once you understand that, it gets pretty simple.

Without actually being able to put hands on, we are all just shooting in the dark.

 

[PNW_Steve]

First of all, if your lgs suggested a heavier buffer to fix a short stroking issue, I'd stop asking them for advise.

I'm gonna guess that this is something that you threw together. The problem could be any number of things. Leaking gas key, bad rings, really bad fit between the barrel and gas block, undersized gas port in the barrel, etc.

First, you need to be using dedicated 300bo mags with subs. They are much longer than supers and will get hung up in a 5.56 pmag or similar mags. Get yourself a proper mag and load one round into it. Chamber the round and fire it. Do this a few times. What happens? Does the bolt lock back on all of them, some of them, none of them? If it doesn't lock back on all of them, my guess would be that you're undergassed. Check gas port size. What size you should have kind of depends on whether you're running supers or subs ... suppressed or unsuppressed. Are you running a traditional can or flow through?

Despite what has become a popular notion, ARs are not just tinker toys. Just because your throw AR parts together and it comes out looking like an AR doesn't mean it's gonna run like it's supposed to and just asking what buffer and spring should I get usually doesn't lead to a solution.

I'm not ranting. I'm just trying to make the point that if you have a true interest, read a book. It will explain what all of the parts do and why. Once you understand that, it gets pretty simple.

Without actually being able to put hands on, we are all just shooting in the dark.

I am running a standard can.

I understand, assembling the parts is only half of the process. Getting everything to play together properly is the other half.

I have some aluminum mags I am going to try.

 

[TonyAngel]

I am running a standard can.

I understand, assembling the parts is only half of the process. Getting everything to play together properly is the other half.

I have some aluminum mags I am going to try.

Man, I really hope that I wasn't coming across as an a$$. It's just a peeve of mine. I totally understand that there are some guys that really do learn by doing and experience is their teacher. I kind of fall into this category, but once I realized how much I didn't even know what I didn't know, I got a book and read it from cover to cover. Once you can visualize all of it in your head, that's when it becomes tinker toys.

Look, for a 300BO rig, assuming that you don't want to use an adjustable gas block, I've found that an ideal place to be with a standard can is to tune the rig to run just right with supers, but just slightly undergassed with subs, meaning that it will cycle, but the bolt won't always lock back on empty. This way, it'll run good with supers, but when you add the can, the added pressure from the can will have it running right suppressed with subs.

Let's just assume that bolt carrier group and gas block are right. That would leave the size of your gas port in question. If you have a selection of drill bits, just move the gas block to the side, or whatever, and find a drill bit that fits snugly in the gas port hole. Now, measure that with a caliper or micrometer. What's your measurement? If memory serves, it should be around .095 or so; UNLESS you got a barrel ported for subs to be run suppressed, in which case, it's gonna do what you described when shooting subs unsuppressed.

Honestly, the sweetest and most versatile running rig I've put together was a 10" with the gas port at .1 and running a RifleSpeed gas block to tame the gas.

In any case, before you go drilling anything, try running one round in a true 300bo mag and see what happens. Actually, when running the one round in the mag, it shouldn't matter what mag you use. We just need to confirm undergassing. BTW, do this with the standard buffer. Or and H1. The H3 is getting a little heavy.

 

[USK308]

+1 on what @TonyAngel said!

Set your AGB to Wide Open (for Superlative Arms, that is 18 clicks / 4.5 turns from closed) and put ONE round in a proper 300BO magazine.

Measuring gas port is also a critical aspect. I have found far too many barrel Mfr's, regardless of AR15/M4 or AR10/LR308 are quite sloppy in their Gas Port sizing. AR15/M4 barrels are less suspect...but there can still be a one-off issue!!!

When I built my 300BO, the first barrel I bought was a Faxon 10.5 barrel. I could not get ANY subsonic ammo to work...AT ALL! I measured the gas port and it was just too large even trying an H3 JP SCS buffer PLUS a stiffer spring on the JP SCS. Note: I do have Magpul 300BO mags, to eliminate any feeding issues with regular Magpul 5.56 mags.

I eventually opted to buy a Rosco Mfg 10.5" barrel and out of the gate, the barrel works flawlessly for 200gr S&B subs or Fiocchi 220gr subs. Hornady ammo is a totally different story where there are a number of conversations on various forums talking about Hornady using lesser powders causing ammo to be a real PITA!

Recently, I decided to build a second upper for my 300BO, using a Rosco 8.2" barrel. I found that the gas port was just a tad small causing failure to eject or failure to lockback with one round in the mag. To resovle I had to drill it out (#43 drill bit to open it up just a smidge). I'll be going to the range tomorrow to confirm functionality. If it still isn't quite there, I will go to a #42 drill bit and that should fix the issue fully.

What does this mean for you, you ask? The solution is there...and the Forum members will help you as best we can, to get your 300BO over the hump!!

 

[WeR0206]

First of all, if your lgs suggested a heavier buffer to fix a short stroking issue, I'd stop asking them for advise.

I'm gonna guess that this is something that you threw together. The problem could be any number of things. Leaking gas key, bad rings, really bad fit between the barrel and gas block, undersized gas port in the barrel, etc.

First, you need to be using dedicated 300bo mags with subs. They are much longer than supers and will get hung up in a 5.56 pmag or similar mags. Get yourself a proper mag and load one round into it. Chamber the round and fire it. Do this a few times. What happens? Does the bolt lock back on all of them, some of them, none of them? If it doesn't lock back on all of them, my guess would be that you're undergassed. Check gas port size. What size you should have kind of depends on whether you're running supers or subs ... suppressed or unsuppressed. Are you running a traditional can or flow through?

Despite what has become a popular notion, ARs are not just tinker toys. Just because your throw AR parts together and it comes out looking like an AR doesn't mean it's gonna run like it's supposed to and just asking what buffer and spring should I get usually doesn't lead to a solution.

I'm not ranting. I'm just trying to make the point that if you have a true interest, read a book. It will explain what all of the parts do and why. Once you understand that, it gets pretty simple.

Without actually being able to put hands on, we are all just shooting in the dark.

+1 on this. Very well said. There are so many variables in play with gas guns. Eliminating as many as you can (such as using proper mags, knowing the gas port size, etc) will help immensely with troubleshooting.

Regular gassers can be hard enough to tune let alone a suppressed 300 BO running subs.

For the visual learners out there here is a nice short video summarizing dwell time and how the gas system works:

 

[TonyAngel]

If youre still having trouble after trying some of what was mentioned here, maybe shoot a little video with the ejection port being the target. In some situations, extreme over gassing could also cause the issues you're having, but I would think if that was the case, other problens would be manifesting themselves.... like torn case rims.

 

[WeR0206]

+1 on what @TonyAngel said!

Set your AGB to Wide Open (for Superlative Arms, that is 18 clicks / 4.5 turns from closed) and put ONE round in a proper 300BO magazine.

Measuring gas port is also a critical aspect. I have found far too many barrel Mfr's, regardless of AR15/M4 or AR10/LR308 are quite sloppy in their Gas Port sizing. AR15/M4 barrels are less suspect...but there can still be a one-off issue!!!

When I built my 300BO, the first barrel I bought was a Faxon 10.5 barrel. I could not get ANY subsonic ammo to work...AT ALL! I measured the gas port and it was just too large even trying an H3 JP SCS buffer PLUS a stiffer spring on the JP SCS. Note: I do have Magpul 300BO mags, to eliminate any feeding issues with regular Magpul 5.56 mags.

I eventually opted to buy a Rosco Mfg 10.5" barrel and out of the gate, the barrel works flawlessly for 200gr S&B subs or Fiocchi 220gr subs. Hornady ammo is a totally different story where there are a number of conversations on various forums talking about Hornady using lesser powders causing ammo to be a real PITA!

Recently, I decided to build a second upper for my 300BO, using a Rosco 8.2" barrel. I found that the gas port was just a tad small causing failure to eject or failure to lockback with one round in the mag. To resovle I had to drill it out (#43 drill bit to open it up just a smidge). I'll be going to the range tomorrow to confirm functionality. If it still isn't quite there, I will go to a #42 drill bit and that should fix the issue fully.

What does this mean for you, you ask? The solution is there...and the Forum members will help you as best we can, to get your 300BO over the hump!!

Rosco makes some damn good barrels for the money. I may grab one for my 6 arc build as a backup. Especially good value when purchased during holiday discount etc

 

[alamo5000]

Hey Everyone,

I am having some trouble sorting out correct buffer spring and weight.

Can anyone point me to a good troubleshooting thread or resource?

I have a 10.5, pistol gas, 300BO. I started with a carbine buffer and spring and had short stroking trouble. At the advice of a LGS, I replaced the carbine buffer with an H3. It still short strokes. Brass ejects but it doesn't pick up another round.

I also have an 18 inch, rifle gas, .223 Wylde that had the same problem.

What do you all recommend?

Thanks

Without actually seeing it function it's hard to tell.

However it sounds like you are going the wrong direction.

If it's actually short stroking then you might need a lighter buffer. Short stroke to me means that the carrier is not coming all the way back which typically means not enough energy getting to the carrier.

Especially with 300blk this is probably the case.

On the other end of the spectrum is having too much gas and pressure getting back to the carrier. Typically this leads to malfunctions because the carrier is moving way too fast and can bounce at both ends of the travel.

In that case adding additional weight counteracts the problem and slows everything down.

Again though it depends on the type of malfunction that you are seeing as to what you need to do.

If it's genuinely because of not enough energy getting to the carrier it could be a gas system problem in addition to the wrong buffer weight.

 

[Jsp556]

If you’re short stroking an adjustable gas block is a waste of money. You need more gas, you don’t want to restrict it.

 

[PNW_Steve]

Regarding the 18" .223 Wylde barrel:

Gas port is .093

 

[WeR0206]

Regarding the 18" .223 Wylde barrel:

Gas port is .093

Hmm that might be a smidge small. I think recommended gas port size for 18” rifle gas is 0.0995 but some others may chime in.

 

[TonyAngel]

Hmm that might be a smidge small. I think recommended gas port size for 18” rifle gas is 0.0995 but some others may chime in.

View attachment 8661852

The published specs from SOLGW are a good guide and I give them kudos for having the nuts to do so. Still, keep in mind that they drill their holes with a certain philosophy in mind with certain ammunition. The philosophy, as near as I can tell, is to have a combat reliable weapon with true milspec ammo.

What this means is that their stuff will run full power ammo with either an A5H2 buffer and rifle spring or an H2 or H3 buffer with a springco blue or red spring. I find this to be a bit of overkill.

Still, my point is that a .093 port on an 18" barrel with rifle gas should be fine. Just don't go too heavy on the spring ir buffer. If it is short stroking, it's something else.

Was the 18" running fine at some point and then started having trouble or has it always had this problem? If the former, check the gas key and rings. If the latter, you have a gas leak or stoppage some place other than in the BCG.

 

[WeR0206]

The published specs from SOLGW are a good guide and I give them kudos for having the nuts to do so. Still, keep in mind that they drill their holes with a certain philosophy in mind with certain ammunition. The philosophy, as near as I can tell, is to have a combat reliable weapon with true milspec ammo.

What this means is that their stuff will run full power ammo with either an A5H2 buffer and rifle spring or an H2 or H3 buffer with a springco blue or red spring. I find this to be a bit of overkill.

Still, my point is that a .093 port on an 18" barrel with rifle gas should be fine. Just don't go too heavy on the spring ir buffer. If it is short stroking, it's something else.

Was the 18" running fine at some point and then started having trouble or has it always had this problem? If the former, check the gas key and rings. If the latter, you have a gas leak or stoppage some place other than in the BCG.

Excellent point. Re: the 223 barrel I told OP upstream to just call the barrel manufacturer and ask them what buffer weight/spring they recommend for his particular barrel based on all their testing, gas port size, dwell time, etc..

If they dont have an answer bc they didn’t do any testing that’s probably a bad sign. If the manufacturer does have a suggestion based on testing and it still doesn’t work then something else is going on as you said. It could be a dozen different things even something as simple as a loose fit between the bolt and bcg due to tolerance stacking. First thing id check though would be gas rings and gas key screws.

 

[TonyTheTiger]

First of all, if your lgs suggested a heavier buffer to fix a short stroking issue, I'd stop asking them for advise.

Haven't read the whole thread, but that stuck out pretty quick.
As long as we're talking about bad advice pet peeves, when someone is having undergassed problems and the peanut gallery collectively suggests an AGB, that winds me up pretty good. AGB's don't add gas beyond the maximum you're already getting with a standard GB. Come on people, use your brains.
And maybe the nuances of subsonic gun tuning are beyond me, but for supersonic stuff, if your gun isn't running at all, a small change in buffer weight won't fix it. And if it does suddenly work, it's gonna be super borderline. But the go-to gunshop counter advice is always to go from an H2 to an H3 or whatever.
Alright, I'm done ranting.

 

[TonyTheTiger]

Excellent point. Re: the 223 barrel I told OP upstream to just call the barrel manufacturer and ask them what buffer weight/spring they recommend for his particular barrel based on all their testing, gas port size, dwell time, etc..

If they dont have an answer bc they didn’t do any testing that’s probably a bad sign.

I think you'd be surprised how many barrel manufacturers just follow the known guidelines and don't really know how to optimize this stuff.

 

[TonyAngel]

Haven't read the whole thread, but that stuck out pretty quick.
As long as we're talking about bad advice pet peeves, when someone is having undergassed problems and the peanut gallery collectively suggests an AGB, that winds me up pretty good. AGB's don't add gas beyond the maximum you're already getting with a standard GB. Come on people, use your brains.
And maybe the nuances of subsonic gun tuning are beyond me, but for supersonic stuff, if your gun isn't running at all, a small change in buffer weight won't fix it. And if it does suddenly work, it's gonna be super borderline. But the go-to gunshop counter advice is always to go from an H2 to an H3 or whatever.
Alright, I'm done ranting.

Yeah, this drives me nuts too. The lesson is ... never ask advise from someone trying to sell you something.

Actually, I'd say that adding an AGB to an undergassed system makes it worse. I haven't seen an adjustable gas block yet that doesn't leak gas from around the adjustment screw(s).

 

[PNW_Steve]

I just pulled the gas block off of the 223 and found a concentric ring of carbon around the gas port. That tells me that the gas block was properly aligned. I looked at the gas key and it looks normal.

 

[WeR0206]

I just pulled the gas block off of the 223 and found a concentric ring of carbon around the gas port. That tells me that the gas block was properly aligned. I looked at the gas key and it looks normal.

Did you check the gas rings and if the gas key screws were loose?

 

[TonyAngel]

I just pulled the gas block off of the 223 and found a concentric ring of carbon around the gas port. That tells me that the gas block was properly aligned. I looked at the gas key and it looks normal.

Just looking at and wriggling the gas key won't tell you anything. You can put a wrench on it and see if the screws tighten any. I think the torque spec is 35 in-lbs.

Still, even if the screws are tight, the mating surface of the key may not be flat allowing gas to escape.

Ok, take this with a grain of salt, since I don't have hands on the rifle. I am assuming that this is a fresh assembly that never ran right. First, check the gas rings. Fully extend the bolt while its in the carrier and stand the BCG up on the face of the bolt. If it falls, retracting the bolt, the rings are bad.

Second, remove the gas key. Clean the mating surface on the bolt carrier. Then, stone the carrier key. Slide the mating surface of the key across a fine grit stone to ensure that it's flat. It shouldn’t take much. I like to use Loctite 680 between the key and the bolt carrier as gasket material. Use red loctite on the screws. Just watch not to get any of that green loctite down in any gas holes.

I suppose I should also mention that I have had occasions where, due to tolerance stacking, some gas tubes just didnt work with some gas keys. Just changing the tube was the fix. In hindsight, changing the gas tube is likely the thing to do if the rings are good.

 

[WeR0206]

Just looking at and wriggling the gas key won't tell you anything. You can put a wrench on it and see if the screws tighten any. I think the torque spec is 35 in-lbs.

Still, even if the screws are tight, the mating surface of the key may not be flat allowing gas to escape.

Ok, take this with a grain of salt, since I don't have hands on the rifle. I am assuming that this is a fresh assembly that never ran right. First, check the gas rings. Fully extend the bolt while its in the carrier and stand the BCG up on the face of the bolt. If it falls, retracting the bolt, the rings are bad.

Second, remove the gas key. Clean the mating surface on the bolt carrier. Then, stone the carrier key. Slide the mating surface of the key across a fine grit stone to ensure that it's flat. It shouldn’t take much. I like to use Loctite 680 between the key and the bolt carrier as gasket material. Use red loctite on the screws. Just watch not to get any of that green loctite down in any gas holes.

I suppose I should also mention that I have had occasions where, due to tolerance stacking, some gas tubes just didnt work with some gas keys. Just changing the tube was the fix. In hindsight, changing the gas tube is likely the thing to do if the rings are good.

+1 on this. I think torque spec (wet) for gas key screws is around 58 in-lbs. One way I like to check gas key screws is to set your torque wrench to around 25 to 30 inch pounds and try to loosen the screws if they break free then they weren’t torqued down properly or have come loose/sheared. Set the torque wrench to 58 inch pounds put a little oil or some type of thread locker on the screws and then torque them down and stake if you have the tool.

See here and here for good videos from SOTAR re: installing gas key on carrier.

 

[TonyAngel]

+1 on this. I think torque spec (wet) for gas key screws is around 58 in-lbs. One way I like to check gas key screws is to set your torque wrench to around 25 to 30 inch pounds and try to loosen the screws if they break free then they weren’t torqued down properly or have come loose/sheared. Set the torque wrench to 58 inch pounds put a little oil or some type of thread locker on the screws and then torque them down and stake if you have the tool.

See here and here for good videos from SOTAR re: installing gas key on carrier.

Yup. I think the milspec torque is 35 or so, but guys that I learned from went heavier. Now that I've thought more about it, I kind of have the feeling that it could be the gas tube.

If the gas key was leaking, you'd see a carbon "ring" type residue develop. What makes me hesitant about pointing at the gas tube is the fact that you're having trouble with two rigs.

@ the OP... you don't happen to be in the New Orleans area, are you? Of you area, send me a DM. I shoot a couple of times a week and frequent the outdoor ranges and I always have my tool bag.

 

[PNW_Steve]

Did you check the gas rings and if the gas key screws were loose?

Yes. All good.

 

[WeR0206]

Yup. I think the milspec torque is 35 or so, but guys that I learned from went heavier. Now that I've thought more about it, I kind of have the feeling that it could be the gas tube.

If the gas key was leaking, you'd see a carbon "ring" type residue develop. What makes me hesitant about pointing at the gas tube is the fact that you're having trouble with two rigs.

@ the OP... you don't happen to be in the New Orleans area, are you? Of you area, send me a DM. I shoot a couple of times a week and frequent the outdoor ranges and I always have my tool bag.

Yes you’re correct milspec is 35 (with hexhead screws). I personally shoot for 50 especially since I only use oil (no thread locker) and grade 8 or better screws.

Speaking of gas key screws I just found this on Amazon, you can get 100 grade 12.9 grade screws for like 8 bucks!

https://a.co/d/iFLNuS5

 

[Top O' Texas]

i'll also agree that a heavier buffer will NOT fix the issue! even with a non-agb and it still short stroking, an agb will NOT help! either reduce the carrier weight and/or reduce the buffer weight. spring pressure will only help against bounce (sometimes), longer (more rounds) use of it and/or help it go into battery. w/o knowing the gas port size it seems to be undersized as not knowing the bcg and buffer weights. i have an 8 and 16" 300bo that i swap uppers on and never change the buffer or spring out for it to run properly. neither have an agb. none ever hosted a suppressor either. does the bcg show signs of leakage or the tube at the gas block? short stroking can be the block nor being aligned. too many possible issues with the info/post i've read.

 

[Top O' Texas]

i check gas rings with air pressure