Tuning a gas gun/false pressure signs

[Dirtracer151]

Hey guys, wanted to see if anyone had any advice to offer regarding tuning my precision AR.

The rifle -
LMT MLR with a converted Proof 18" 223 barrel
Rifle speed adjustable gas block
Carbine buffer and spring
LMT BCG
TBAC Ultra 7 or 5 suppressor

load-
LC brass, CCI 400, 77smk, 23.3gr 8208 xbr, 2.256 OAL
2800fps (garmin verified)

I primarily use 8208 for my 223 loads in AR and bolt gun. I love the speed it gives me while maintaining excellent temp stability and accuracy. I've been running on a few jugs i got pre covid and have struggled to find any replenishments. Was finally able to score some from Brownells last month. Decided to open the new stuff to test it and see how the velocity compared to the old stuff. I used the exact same components, loaded back to back, and fired back to back. To my surprise the new powder is running 180fps slower than the old stuff. Accuracy is still great but 180fps!!!!

A call to Hodgdon and the tech guy tells me it sounds normal and 180fps is well within acceptable. Especially since im in AZ and its so dry here and that's why the old stuff is fast (i don't remember it being slow before but i know 2800 is really fast for this load and barrel length). His recommendation is to just dump more powder

i explained to him that both set of loads show the exact same pressure signs regardless of the velocity (semi round primers/light ejector swipes) I'm afraid to stuff 180fps worth of the new powder in the cases to achieve more velocity. I'm able to run up to 24.0gr in my bolt gun with no issues although i've found 23.5-23.8 is the sweet spot for accuracy there.

I'm wondering if I'm seeing some false pressure signs on the brass. The swipes are very light. There's no deep impression into the ejector like I've seen in the past with different loads/rifles. There really isn't an impression at all...its just a shiney swipe with a very small burr. The primers still have enough rounded edges I'm comfortable giving it more in that department but the swipes throw me off. I don't see any extractor pull marks whatsoever.

My question revolves around my setup. Since i have the adjustable gas block i originally thought it would be fun to make it extra gamer and throw a carbine buffer in it for low reciprocating mass and buttery smooth recoil and then just adjust gas as needed. The objective was definitely achieved as its a ton of fun to shoot and very accurate. I'm thinking now that maybe a heavier buffer and/or a stiffer spring might be needed to hold that bolt closed a hair longer and adjust the gas block to that instead and it would maybe reduce the swipes and allow a bit more powder/pressure? I read some places that say buffer weight and gas block do the same thing though. Its kinda confusing. Should i actually be running the heaviest setup i possibly can for hot/fast loads to keep the bolt closed longer? Or does the adjustable gas block achieve the same result and a carbine buffer and spring is fine? It almost feels like pressure wise I'm fine but I'm seeing the swipes because the bolts trying to unlock too soon. Does a JP bolt help here? I've read that their ejectors are tuned to help with the swipes.

Ideally i want this new lot of powder to go faster than 2630fps. His point about the old powder drying out is valid but 180fps seems like there's more to it than just that.

Thanks for any words of wisdom.

 

[Cascade Hemi]

Open the powder and let it sit for a week unsealed. You're probably experiencing a humidity variance between the climate they packed the powder in and your dry climate.

 

[eklarsen]

Well, when you say your suppressor is 5 or 7 that can be 100 or so fps right there 2 inches more barrel was your test with the 5 or the 7?

 

[Dirtracer151]

Well, when you say your suppressor is 5 or 7 that can be 100 or so fps right there 2 inches more barrel was your test with the 5 or the 7?

Test was done with the ultra 5

 

[FredHammer]

Hey guys, wanted to see if anyone had any advice to offer regarding tuning my precision AR. I offer advice, but do expand all the "click to expand" sections to see it. Some formatting issues here.

The rifle -
LMT MLR with a converted Proof 18" 223 barrel
Rifle speed adjustable gas block
Carbine buffer and spring
LMT BCG
TBAC Ultra 7 or 5 suppressor

load-
LC brass, CCI 400, 77smk, 23.3gr 8208 xbr, 2.256 OAL Busting you balls here, but how did you come about 2.25(6) and not 2.255?
2800fps (garmin verified) That's 50fps faster than just about all Mk262 clones, if not MK262 actual. Maybe you are higher elevation too.

I primarily use 8208 for my 223 loads in AR and bolt gun. I love the speed it gives me while maintaining excellent temp stability and accuracy. I've been running on a few jugs i got pre covid and have struggled to find any replenishments. Was finally able to score some from Brownells last month. Decided to open the new stuff to test it and see how the velocity compared to the old stuff. I used the exact same components, loaded back to back, and fired back to back. To my surprise the new powder is running 180fps slower than the old stuff. Accuracy is still great but 180fps!!!! That's a kick in the pants, but not uncommon. Hodgdon has 3 different variants of H100V out there too.

A call to Hodgdon and the tech guy tells me it sounds normal and 180fps is well within acceptable. Fucking of course they'll say that.

Especially since im in AZ and its so dry here and that's why the old stuff is fast (i don't remember it being slow before but i know 2800 is really fast for this load and barrel length). His recommendation is to just dump more powder Well, if it's running slower burn rate, why not?!

i explained to him that both set of loads show the exact same pressure signs regardless of the velocity (semi round primers/light ejector swipes) I'm afraid to stuff 180fps worth of the new powder in the cases to achieve more velocity. I'm able to run up to 24.0gr in my bolt gun with no issues although i've found 23.5-23.8 is the sweet spot for accuracy there.

I'm wondering if I'm seeing some false pressure signs on the brass. The swipes are very light. There's no deep impression into the ejector like I've seen in the past with different loads/rifles. There really isn't an impression at all...its just a shiney swipe with a very small burr. The primers still have enough rounded edges I'm comfortable giving it more in that department but the swipes throw me off. I don't see any extractor pull marks whatsoever. So, try this method to look at pressure signs...decap the primer and look at them from the side. If they hourglass from middle to top, the anvils fall out or are disintegrated, or there is black residue creeping up the sides you are over pressure. If they deacap easily and your primer pocket dia measures over .076 (Typical dia of SRP) you are over pressure.

My question revolves around my setup. Since i have the adjustable gas block i originally thought it would be fun to make it extra gamer and throw a carbine buffer in it for low reciprocating mass and buttery smooth recoil and then just adjust gas as needed.

I've typically heard this phrase pertaining to the BCG low mass. Never the buffer weight.

The objective was definitely achieved as its a ton of fun to shoot and very accurate. I'm thinking now that maybe a heavier buffer and/or a stiffer spring might be needed to hold that bolt closed a hair longer and adjust the gas block to that instead and it would maybe reduce the swipes and allow a bit more powder/pressure?

Yup H2, or Vltor A5 system for that last bit of ejector swipe removal more times than I can count.

I read some places that say buffer weight and gas block do the same thing though. Its kinda confusing. Should i actually be running the heaviest setup i possibly can for hot/fast loads to keep the bolt closed longer? Or does the adjustable gas block achieve the same result and a carbine buffer and spring is fine? It almost feels like pressure wise I'm fine but I'm seeing the swipes because the bolts trying to unlock too soon. Does a JP bolt help here? I've read that their ejectors are tuned to help with the swipes.

Gas regulation is 95% of the equation, buffer weight the minimal rest of the equation to balance out the pressure.

Ideally i want this new lot of powder to go faster than 2630fps. His point about the old powder drying out is valid but 180fps seems like there's more to it than just that.

I've got 20-25yr old Varget that has always been faster burning than what people are commonly posting online in recent years in regards to their powder charges. Sample size one anecdotal experience here, but makes this notion plausible to me.

Thanks for any words of wisdom.

 

[Torchy]

I'm kind of in the same boat as your OP.

Bartlein barrel 20'', rifle gas, 22.0 gr of 8208, cci450, Thunderbeast ultra 7 in .223 direct thread.

I have a SLR AGB tuned to perfection.

Running a Geissele H1 buffer/braided spring combo.

Only thing I can think of is to add weight to my buffer.

Getting light ejector swipe and semi flat primers. Pretty dirty brass. I am ejecting at 3 o'clock. No/very minimal extractor marks. It's a new barrel and not shooting good like 1.5-2moa. I have bedded the barrel extension to the matched Seekings receiver set. Rail isn't impacting GB, 50 rounds down the tube so far.

I can see a little not to good looking erosion/divot at the gas port with my hawkeye borescope but have no way to take a pic of it. Copper is filling the divot.

At a loss some.

 

[FredHammer]

I can see a little not to good looking erosion/divot at the gas port with my hawkeye borescope but have no way to take a pic of it. Copper is filling the divot.

At a loss some.

Normal. There is gas port metal migration of every barrel. 416R shows it ugly and quicker than CMV 4150 or nitrided barrels. Give it 125-150rnds and don't shit your pants at group sizes till then. You can accelerate the break in by smoothing that gas port metal migration with Thorroclean every 30rnds. Or Iosso paste with a heavy amount of gun oil to suspend the Iosso.

 

[mettee]

TBAC cans create a lot of back pressure.

If you have a regular carbine buffer weight that won't be enough in this combo. Leave the spring alone and try the heaviest buffer you can get.

You will obviously need to know two gas settings if you shoot un-suppressed, the heavy buffer will actually make it recoil softer than the carbine buffer in either config, unless you put a heavy spring in as that will create more issues/unwanted forces. Try the buffer first then decide what to do based on the feedback you get from the rifle.

You don't need any special bolts either.

I wouldn't throw more powder, I do think allowing the powder to "climatize" is a good idea.

Post pics of your brass, side view, and the heads.

 

[mettee]

I'm kind of in the same boat as your OP.

Bartlein barrel 20'', rifle gas, 22.0 gr of 8208, cci450, Thunderbeast ultra 7 in .223 direct thread.

I have a SLR AGB tuned to perfection.

Running a Geissele H1 buffer/braided spring combo.

Only thing I can think of is to add weight to my buffer.

Getting light ejector swipe and semi flat primers. Pretty dirty brass. I am ejecting at 3 o'clock. No/very minimal extractor marks. It's a new barrel and not shooting good like 1.5-2moa. I have bedded the barrel extension to the matched Seekings receiver set. Rail isn't impacting GB, 50 rounds down the tube so far.

I can see a little not to good looking erosion/divot at the gas port with my hawkeye borescope but have no way to take a pic of it. Copper is filling the divot.

At a loss some.

Less spring more buffer.

 

[mettee]

Think about it like this:

"What is the spring actually doing?"

"And what is the buffer actually doing?"

Break their functions down seperately and think about what each part does and what the basic physics are behind each part.

In one aspect the spring when deformed stores energy and in the other it releases that same stored energy which is potential energy.

The buffer is just that, try moving Andre the Giant or Richard Simmons, one moves much easier when force is applied You just need to supply the right amount of resistance to the initial push(force) of gas that happens more aggressively when suppressed.

I'm ignoring gas adjustment but that will be part of this. I feel like everyone know how to adjust for lock back.

 

[BuildingConceptsllc]

As others have said about the powder, just leave the lid off or a week , shake it up, leave the lid off a few more days and it should get a lot closer to your old stuff.

 

[supercorndogs]

When you dry the powder. It will be lighter and you will be adding more.

 

[Clint H]

Couple dumb questions:

Rifle length gas system, I'm guessing? Or mid length?

Standard weight BCG? Or lightweight?

What does the ejection pattern look like? 3-4 o'clock or more like 1-2 o'clock?


Just off-hand, I'd say go up on the buffer weight one increment and turn down the gas block until you get a good ejection pattern, then check again. It does sound like the bolt is unlocking before the pressure has fully vented.

Could possibly be an excessive headspace issue, too. That can cause the cartridge to slam back into the ejector. I'd start with the buffer weight, though.

 

[Dirtracer151]

Couple dumb questions:

Rifle length gas system, I'm guessing? Or mid length?

Standard weight BCG? Or lightweight?

What does the ejection pattern look like? 3-4 o'clock or more like 1-2 o'clock?


Just off-hand, I'd say go up on the buffer weight one increment and turn down the gas block until you get a good ejection pattern, then check again. It does sound like the bolt is unlocking before the pressure has fully vented.

Could possibly be an excessive headspace issue, too. That can cause the cartridge to slam back into the ejector. I'd start with the buffer weight, though.

Rifle gas

Standard LMT BCG

Ejection is about 4 o clock. Gas block dialed to hold back on last round but not much more.

I'm thinking I do need to up the buffer weight and re adjust the gas as needed the more I've thought about it.

Definitely not a headspace issue

 

[Clint H]

Rifle gas

Standard LMT BCG

Ejection is about 4 o clock. Gas block dialed to hold back on last round but not much more.

I'm thinking I do need to up the buffer weight and re adjust the gas as needed the more I've thought about it.

Definitely not a headspace issue

And no other pressure signs? (Pierced, popped, or flattened primers)

Yeah, I'd switch up the buffer weight then and re-try. I had a large-frame 308 with a carbine H2 that was doing the same thing. I was at a very modest load, so knew I wasn't over-pressuring. As soon as I changed to an H3, the brass started coming out clean.

Edit: clarity

 

[Cascade Hemi]

Rifle gas

Standard LMT BCG

Ejection is about 4 o clock. Gas block dialed to hold back on last round but not much more.

I'm thinking I do need to up the buffer weight and re adjust the gas as needed the more I've thought about it.

Definitely not a headspace issue

I'd probably run an H buffer with that set up but your load is way over pressure. Regardless of the new powder, you have pressure signs because you have too much pressure.

 

[supercorndogs]

Is there a bur on or is your ejector hole unchamfered or sharp?

 

[Dirtracer151]

And no other pressure signs? (Pierced, popped, or flattened primers)

Yeah, I'd switch up the buffer weight then and re-try. I had a large-frame 308 with a carbine H2 that was doing the same thing. I was at a very modest load, so knew I wasn't over-pressuring. As soon as I changed to an H3, the brass started coming out clean.

Edit: clarity

Nadda, the rims look great and I can't even tell where there were in contact with the extractor. No pops, no primers laying in the trigger group. Primers are flat but have rounded edges. I would consider the load with the old powder to be a comfortable max load.

I'd probably run an H buffer with that set up but your load is way over pressure. Regardless of the new powder, you have pressure signs because you have too much pressure.

I mean maybe... the old powder is .1gr over Hodgdons max. I'm feeling pretty comfortable right there with the old powder. The weird part is the new stuff being so much slower yet showing the same signs on brass

Is there a bur on or is your ejector hole unchamfered or sharp?

That was also a consideration. There's nothing I can see but I was gonna bring a couple spare bolts next time I went out and do some swapping.

 

[frame12]

Didn't read anyone else's comments but saw "CCI400".

CCI says not to use the 400 in a gas gun. While I haven't had any issues with .223/556, in my 6.5 Creed they puncture at very safe pressures.
The 450's are thicker, as are the BR's. If you can, stick with the white box primers or Fed AR primers.
I had a slam fire on a 450 during a competition a couple months ago. Since then I switched to Fed AR match SRPs.

 

[MontanaMan]

If you purely want to evaluate pressure (as best you can from signs on the case & primer) shut off the gas entirely, make the gun a single shot & evaluate the brass & primer accordingly.

Things like swipes are a function of the rest of the equation..............timing, buffer & BCG weight, gas tuning, etc.

MM

 

[FredHammer]

If you purely want to evaluate pressure (as best you can from signs on the case & primer) shut off the gas entirely, make the gun a single shot & evaluate the brass & primer accordingly.

Things like swipes are a function of the rest of the equation..............timing, buffer & BCG weight, gas tuning, etc.

MM

Fucking A! KISS and isolate the variables in the process. Manipulate the parts to function on the closed gas safe pressure load developed round.

 

[Dirtracer151]

If you purely want to evaluate pressure (as best you can from signs on the case & primer) shut off the gas entirely, make the gun a single shot & evaluate the brass & primer accordingly.

Things like swipes are a function of the rest of the equation..............timing, buffer & BCG weight, gas tuning, etc.

MM

Yep that makes total sense. I'm not overly worried about the primers so I think it is a timing issue or a sharp edge on the bolt somewhere. I will shut it off just to confirm. Haven't had a chance to make it back out with holidays etc.

 

[Cascade Hemi]

I mean maybe... the old powder is .1gr over Hodgdons max. I'm feeling pretty comfortable right there with the old powder. The weird part is the new stuff being so much slower yet showing the same signs on brass

Not maybe. Velocity is directly correlated to pressure. You chronographed your 18" barrel producing greater velocity than Hodgdon's 24" barrel.

Your search returned 1 loads
Twist: 1:12.000"

Barrel Length: 24.000"

Trim Length: 1.750"
Bullet: 77 GR. SIE HPBT

Diameter: 0.224"

Case: Winchester

Primer: Winchester SR, Small Rifle

Starting Load

Maximum Load

Availability

Manufacturer

Powder

C.O.L.

Grs.

Vel. (ft/s)

Pressure

Grs.

Vel. (ft/s)

Pressure

IMR

IMR 8208 XBR

2.260"

20.5

2,535

41,800 PSI

23.2

2,792

55,000 PSI

Out Of Stock