Confusing 6ARC AR15 Gas Issue After Switching to Rifle +1 Barrel

[TheyCallMe64]

Hi all - I have a confusing issue that I'd like some guidance on. Getting conflicting answers from the internet and the people I've talked to.

I bought a CMMG Endeavor 300 (never again) in 6mm ARC. The barrel was trash and so was the upper, so I quickly got a new upper and a Proof Research 20" stainless barrel. New barrel shoots lights out. The rifle has an adjustable gas block. Originally the rifle had a rifle length gas system. The new Proof barrel is a rifle +1 gas system. It has a Magpul PRS 3 stock with a rifle length buffer & buffer spring - NOT a carbine length.

It cycles fine with factory ammo, and with LeverEvolution & CFE223 handloads. These produce......acceptable accuracy, but nothing great. I've had much better luck with Varget and 8208XBR for both accuracy and consistent velocities. The results are seriously impressive and I'd like to continue with those loads. However, those loads won't cycle the rifle, even after I load a high enough charge that I see concerning pressure signs. They will eject the spent brass, but won't send the bolt carrier group back far enough to load the next round. The AGB is wide open and is not restricting gas. They will work fine when the barrel is suppressed. And no, I don't really want to "just shoot suppressed all the time, bro."

I tried reducing the number of weights in the buffer, but nothing happened. The guys at Proof said I needed to try a heavier buffer spring before drilling a larger gas port in the barrel - and not a lighter buffer. They said a heavier spring will increase dwell time and thus allow the lower pressure powders to build up more pressure.

A tech at Brownells said "No, that's wrong - a spring won't do it. You need a heavier buffer. But sorry, we don't offer a heavier rifle length one." So I talked to Clint at HeavyBuffers.com and he recommended shortening the buffer tube to a carbine length buffer tube with a spacer, then installing his heavier carbine buffer and spring.

I'm getting tired of sinking time and money into this with no clear answer.

Has anyone experienced a similar issue? Is there a simple solution to this that I'm missing?


UPDATE Sunday, Feb. 19, 2023:

I removed my 5.5 oz rifle length buffer, installed a spacer to shorten it to a carbine length buffer tube system, and had the following results with the adjustable gas block wide open:


-(UNSUPPRESSED) Heavy buffer and spring combination from www.heavybuffers.com (6.4oz buffer) at the recommendation of the guy at Brownells: Ejected, short stroke, failure to lock back or to load the next round.


-(SUPPRESSED) Heavy buffer and spring combination from www.heavybuffers.com (6.4oz buffer) at the recommendation of the guy at Brownells: Ejected, successfully loaded the next round.


-(UNSUPPRESSED) Buffer spring and H1 buffer that came stock with my Daniel Defense DDM4V5. Assuming spring is a standard carbine spring. Ejected, short stroke, failure to lock back or to load the next round.


-(SUPPRESSED) Buffer spring and H1 buffer that came stock with my Daniel Defense DDM4V5. Assuming spring is a standard carbine spring. Ejected, short stroke, failure to lock back or to load the next round.

Surprised this one did not work suppressed.


TL;DR, problem persists and was not overcome.


Next steps to try in the coming week:

1) Replace gas rings on bolt

2) Try a JP silent captured buffer spring with the spring kits of varying strengths, and

3) Try my H1 buffer with a Sprinco yellow spring.

If none of these prove satisfactory, and if no other viable solution presents itself on this forum or in my brain, I'm sending the barrel back to Proof for gas hole enlargement.



UPDATE 2/21/23

-Installed new gas rings on bolt. Ensured gas block was wide open. Test fired. Failure to load next round; failure to lock back on last round.

-Installed JP Enterprises Silent Capture Spring system. Test fired. Failure to load next round; failure to lock back on last round.

-Installed JP Enterprises reduced power spring (white). Test fired. Failure to load next round; failure to lock back on last round.

-Bore scoped barrel; confirmed that gas block is properly in line with gas hole.

At this time, I believe I've exhausted all likely options, and I don't think the Sprinco reduced power spring will yield any wildly better results than the JP reduced power spring.

Therefore, I will pursue opening up the gas hole and report back.

 

[Clayman]

What upper, bcg and agb?

Might be a gas efficiency issue.

Is the gas block leaking a significant amount? From the gas tube or journal.
Was the gas block loose fitting on the gas block journal or was it tight/thermal fit?
It's 100% properly aligned, didn't walk or anything?
Bcg isn't leaking from the gas key? Gas rings appear fine?

Buffers and springs may fix your issue. It's hard to diagnose without seeing it.

I personally use the vltor A5 system with a sprinco green.

 

[TheyCallMe64]

What upper, bcg and agb? The upper is one my gunsmith had lying around, not sure. The bolt carrier is the same one that came with the rifle from CMMG - so is the gas block. I happen to know the gas block is made by SLR and has something like 12 or 15 click positions.

Might be a gas efficiency issue.

Is the gas block leaking a significant amount? From the gas tube or journal. It is not.
Was the gas block loose fitting on the gas block journal or was it tight/thermal fit? Good tight fit. My gunsmith installed it; another gunsmith buddy and I checked it later.
It's 100% properly aligned, didn't walk or anything? That's right. We confirmed it's tight and aligned straight.
Bcg isn't leaking from the gas key? Gas rings appear fine?Don't believe the key is leaking. Rings are indeed getting worn. I will need to replace them. But the rifle only has 800-ish rounds on it, and it's had this issue for a long time. Like, before the rings were getting worn. So I don't think the rings are the problem.

Buffers and springs may fix your issue. It's hard to diagnose without seeing it. Agreed that it's hard to diagnose without seeing it. Not sure who else to talk to.

I personally use the vltor A5 system with a sprinco green. I'm not familiar with those but will look them up.

Thank you for responding. My answers are highlighted above.

 

[jb0311]

^this. It could be a number of things between your gas block all the way back to your buffer spring. I could have missed it, but what direction is it ejecting brass?

 

[TonyTheTiger]

Assuming you don't have any gas block misalignment issues or leaks, sounds to me like you need to try lighter buffer, spring or bolt carrier. Or a combination of the above. Start by running your buffer without any weights and see what happens.

 

[TheyCallMe64]

Assuming you don't have any gas block misalignment issues or leaks, sounds to me like you need to try lighter buffer, spring or bolt carrier. Or a combination of the above. Start by running your buffer without any weights and see what happens.

This is where I start to get confused, since some people (the folks at Proof, Brownells, etc) tell me to run a heavier buffer, spring, or combo and others tell me to reduce the weight of the buffer, spring, or combo that I have.

I did not try running it completely without weights. However, I did cut out 3/4 of the weights and filled it with light foam padding, and the issue was no less apparent.

​

@jb0311 I will test and find out; don't remember which direction it was ejecting with those undergassed loads specifically. The other powders seemed to eject straight out to the right side.

 

[Precision Underground]

This is where I start to get confused, since some people (the folks at Proof, Brownells, etc) tell me to run a heavier buffer, spring, or combo and others tell me to reduce the weight of the buffer, spring, or combo that I have.

I did not try running it completely without weights. However, I did cut out 3/4 of the weights and filled it with light foam padding, and the issue was no less apparent.

​

@jb0311 I will test and find out; don't remember which direction it was ejecting with those undergassed loads specifically. The other powders seemed to eject straight out to the right side.

Are you shooting the same bullet with the ammo that cycles fine and the ammo that doesn’t? What bullet/s and velocities are you shooting? Does the bolt lock back on empty mag when it’s cycling correctly?

You said it works fine suppressed so I doubt this is the issue, but too MUCH gas can cause the carrier to miss the next round.

 

[jb0311]

This is where I start to get confused, since some people (the folks at Proof, Brownells, etc) tell me to run a heavier buffer, spring, or combo and others tell me to reduce the weight of the buffer, spring, or combo that I have.

I did not try running it completely without weights. However, I did cut out 3/4 of the weights and filled it with light foam padding, and the issue was no less apparent.

​

@jb0311 I will test and find out; don't remember which direction it was ejecting with those undergassed loads specifically. The other powders seemed to eject straight out to the right side.

I'd be interested to hear what you find out. Generally you'd want it between 3-4o'clock unsuppressed which would generally put you between 2-3o'clock suppressed (depending on the suppressor of course).

If it's undergassed, running a heavier gas system (bcg, buffer, spring) would send you in the wrong direction. As @Precision Underground mentioned, if you are severely overgassed it could be skipping over the next round but the ejection pattern should tell you which. Might have to have someone watch you or use your camera video in slow mo.

 

[TheyCallMe64]

Are you shooting the same bullet with the ammo that cycles fine and the ammo that doesn’t? What bullet/s and velocities are you shooting? Does the bolt lock back on empty mag when it’s cycling correctly?

You said it works fine suppressed so I doubt this is the issue, but too MUCH gas can cause the carrier to miss the next round.

Thanks for responding. Yes, all Hornady 108 ELDM. When it's cycling properly, yes, it locks back as it should - both with factory loads and handloads of CFE & Lever. It does not lock back when using the same bullet/case/primer with Varget or 8208XBR. Here's a link to my velocities in depth. In the post, I said I didn't see pressure signs, but looking back at the brass I'm pretty sure I do.


I tried choking the gas off intermittently without success.

 

[Mike_in_FL]

When you removed the weights from the buffer, did you give it more gas or left it the same? If the AGB is adjusted wide open and it still doesn't work, the port is too small, or you've got a leak. Let's assume no leak. Your velocities are 200 fps lower with Varget and 8208 so less pressure, rather understandable.

I'd try taking out all the weights as was suggested and getting the yellow spring from Sprinco. I don't know why Brownells or whoever would suggest heavier components. You don't have enough gas to move the mass as it is.

 

[hlee]

I have a 22 Grendel with a +2 rifle gas system. I started with a heavy JP SCS and standard weight spring. I had the same symptoms as you. I replaced the tingsten weights with steel weights and the symptoms disappeared. Based on this, I suggest reducing the weight of your buffer.

 

[Precision Underground]

Thanks for responding. Yes, all Hornady 108 ELDM. When it's cycling properly, yes, it locks back as it should - both with factory loads and handloads of CFE & Lever. It does not lock back when using the same bullet/case/primer with Varget or 8208XBR. Here's a link to my velocities in depth. In the post, I said I didn't see pressure signs, but looking back at the brass I'm pretty sure I do.


I tried choking the gas off intermittently without success.

Yea you’re 100+fps slower and it seems like you need more gas.
What I’d do-
Borescope the barrel and make sure the barrel/block gas holes are lined up perfectly. It doesn’t take much to cover 1/3 of the hole if it’s not lined up just right.
Lower the CFE and Lever charges to land in the same velocity range as the varget groups were and see if you get the same accuracy. Shoot from 2500 to 2650 and see what you get. If you’re only going off a few groups that had a MS hanging on the barrel you may have skewed data. Don’t start drilling on a barrel or buying parts off a couple of groups on a single day.

 

[TheyCallMe64]

When you removed the weights from the buffer, did you give it more gas or left it the same? If the AGB is adjusted wide open and it still doesn't work, the port is too small, or you've got a leak. Let's assume no leak. Your velocities are 200 fps lower with Varget and 8208 so less pressure, rather understandable.

I'd try taking out all the weights as was suggested and getting the yellow spring from Sprinco. I don't know why Brownells or whoever would suggest heavier components. You don't have enough gas to move the mass as it is.

Left it the same, then adjusted it all the way closed, then incrementally opened it up until it was wide open. Tested at each point and it wouldn't cycle.

You're right that that they're lower velocities. A few things to keep in mind: Hornady's reloading manual says they hit pressure at 2400 fps and 26.7 grains with Varget. I was running 2537 fps at the peak and 26.9 grains of powder. Do with that what you will.

Does this look like pressure? Do I need to just keep increasing the charge?

The Varget groups from the post above are in order, left to right (column 1 of brass is 26.0 grains, column 2 is 26.3 grains, etc all the way up to 26.9). I took a photo and a video with a light swirling around to try to show the marks better. Primers look ok to be but brass looks chewed up, and I'm not experienced at reading brass pressure signs in an AR.

Brownells and Proof both said to go heavier because they say I'm not getting enough dwell time with the longer gas system to build up cycling pressure with a calmer powder. Thus, they say I need something heavier to let the pressure build more. That sounds sensible to me on one hand, but so does the counter argument that a lighter system will cycle more easily.

Edit: Sorry guys, you are all helpful and enthusiastic. I appreciate the responses even if I can't respond to them in the right order because they come in while I'm typing a comment.

 

[TonyTheTiger]

Brownells and Proof both said to go heavier because they say I'm not getting enough dwell time with the longer gas system to build up cycling pressure with a calmer powder. Thus, they say I need something heavier to let the pressure build more. That sounds sensible to me on one hand, but so does the counter argument that a lighter system will cycle more easily.

That's straight nonsense, but springs are cheap, buy a heavy one just to prove them wrong.

 

[TheyCallMe64]

I have a 22 Grendel with a +2 rifle gas system. I started with a heavy JP SCS and standard weight spring. I had the same symptoms as you. I replaced the tingsten weights with steel weights and the symptoms disappeared. Based on this, I suggest reducing the weight of your buffer.

Fair enough, I guess I'll try again. What do you recommend for a lighter rifle-length buffer?

Yea you’re 100+fps slower and it seems like you need more gas.
What I’d do-
Borescope the barrel and make sure the barrel/block gas holes are lined up perfectly. It doesn’t take much to cover 1/3 of the hole if it’s not lined up just right.
Lower the CFE and Lever charges to land in the same velocity range as the varget groups were and see if you get the same accuracy. Shoot from 2500 to 2650 and see what you get. If you’re only going off a few groups that had a MS hanging on the barrel you may have skewed data. Don’t start drilling on a barrel or buying parts off a couple of groups on a single day.

Pretty confident it's aligned right; will confirm again using your method though. The CFE and Lever loads were worked up to from much lower in previous tests without the Magneto and weren't any better unfortunately. You're giving good advice for sure. But I have indeed been down that road.
I think this whole issue comes down to: It feels undergassed like you said. I don't know how to get more gas when I'm well over the velocity associated with max pressure in the reloading manual without drilling that hole bigger. It seems like I'm hitting pressure signs, but you can be the judge of that from my comment above.

Guess it's time to try a lighter spring, buffer, or just tell them to drill the hole bigger.

That's straight nonsense, but springs are cheap, buy a heavy one just to prove them wrong.

Fair enough - Y'all have recommended a few good brands for springs so I'll try this too. Thanks

 

[hlee]

Fair enough, I guess I'll try again. What do you recommend for a lighter rifle-length buffer?

Well, you could knock out the pin that holds the rubber tip on your buffer, buy replacement steel and aluminum weights and mix and match until you dial it in…

As I said, I am using a JP silent capture spring in that rifle. Highly recommend, but it is spendy. It works with either a carbine or rifle tube, adding a delrin spacer (included) in a rifle tube.

 

[TheyCallMe64]

Well, you could knock out the pin that holds the rubber tip on your buffer, buy replacement steel and aluminum weights and mix and match until you dial it in…

As I said, I am using a JP silent capture spring in that rifle. Highly recommend, but it is spendy. It works with either a carbine or rifle tube, adding a delrin spacer (included) in a rifle tube.

Yeah, I did that and removed most of the tungsten and steel weights in mine. Ah well. I'll try something. Maybe that JP. Lots of people are very positive about them.

 

[Precision Underground]

Fair enough, I guess I'll try again. What do you recommend for a lighter rifle-length buffer?


Pretty confident it's aligned right; will confirm again using your method though. The CFE and Lever loads were worked up to from much lower in previous tests without the Magneto and weren't any better unfortunately. You're giving good advice for sure. But I have indeed been down that road.
I think this whole issue comes down to: It feels undergassed like you said. I don't know how to get more gas when I'm well over the velocity associated with max pressure in the reloading manual without drilling that hole bigger. It seems like I'm hitting pressure signs, but you can be the judge of that from my comment above.

Guess it's time to try a lighter spring, buffer, or just tell them to drill the hole bigger.



Fair enough - Y'all have recommended a few good brands for springs so I'll try this too. Thanks

Ahh. I was going off the Reddit post that said you had the MS on the barrel for the test. It sounded like you shot them all that day. I’d recommend against putting more powder in the case to try to make it cycle.

 

[Mike_in_FL]

Left it the same, then adjusted it all the way closed, then incrementally opened it up until it was wide open. Tested at each point and it wouldn't cycle.

I wouldn't tell you to increase your charges. I believe you said initially that these are your accuracy loads, they just don't cycle.

So if you reduce the mass of the reciprocating parts the gun should cycle with the gas it has. If it doesn't cycle with the gas block wide open, then it needs a larger port.

The only thing the sales people got right was yes, you have a shorter dwell time. Whenever you step out with extended gas systems you're probably going to have to tune them or at least that's been my experience.

 

[GONE BAD]

Ok, just throwing this out there.
1. What size is the gas port?
2. What is the actual length of
gas tube?
3. Is the gas tube an Armalite
plus1" or a regular mil-spec
plus1" tube.
Some manufacturers use
Armalite specs which are a
little longer.
4. 8208 does not build
pressure as fast as others
so I would expect you need
more dwell time?

 

[Maxduty]

Stick some quarters behind the buffer spring. Should stiffen up the spring and increase your dwell time. Simple to check and remove if not it.

 

[Constructor]

CFE and Lever are slower burning than the other powders so the pressure is higher at the port. If you don't have enough gas at the port with faster powders then heavier springs or buffers would make it worse. No idea what they are thinking when they say go to a heavier buffer or spring.
If it was me I would reduce weight in the buffer like HLEE said or open the port by .003-.004" depending on how drill bit sizing falls. If it has a .086 now step up to a .089, if it has a .089 then increase to a .093, if it has a .093 increase to a .096".
A 20" rifle gas 223 needs a .093, 1" extended would need a .096"-.098. The 6 ARC has more powder capacity than a 223/5.56 but does not create as much pressure so that kind of evens it out and should take close to the same size as a 223/5.56.

 

[TheyCallMe64]

Thanks all, lots of good ideas and several different opinions here. I don't know the answers to all your questions but will test what I can and report back. Very grateful for all the responses.

 

[TheOE800]

Proof spec GP for the 20” rifle +1 gas 6 ARC is .093, basically the standard rifle length/Colt port spec for .223/5.56mm. It comes down to you are so overgassed that carrier speed is exceeding the magazine’s ability to feed the next cartridge or you are so undergassed as to be short-stroking; the symptoms of either condition present similarly.

Now I’m no expert and my words are worth what you paid for them. Haven’t read it all, have you tried a reduced power spring? Fairly cheap part to try. If your dwell time is too short you would need to delay unlocking so I can see why there would have been suggestions for heavier buffer or more spring, but symptoms read like the reciprocating mass is too heavy so I wouldn’t want to add buffer. Also never forget dumb ancillary malfunctions or tolerance stacking in other parts of the system that can impact an already delicate (read: less robustly gassed) rifle: magazine geometry, presentation of magazine, increased drag resultant from alignment issues in the recoil assembly, increased locking/unlocking drag due to alignment issues in the upper assembly, drag on the carrier from the hammer (need more buffer spring for that?).

Your PRS3 should have a spacer to use regular carbine recoil assembly components. Make sure you use that when trying the shorter carbine buffers and springs.

 

[TheyCallMe64]

Proof spec GP for the 20” rifle +1 gas 6 ARC is .093, basically the standard rifle length/Colt port spec for .223/5.56mm. It comes down to you are so overgassed that carrier speed is exceeding the magazine’s ability to feed the next cartridge or you are so undergassed as to be short-stroking; the symptoms of either condition present similarly.

Now I’m no expert and my words are worth what you paid for them. Haven’t read it all, have you tried a reduced power spring? Fairly cheap part to try. If your dwell time is too short you would need to delay unlocking so I can see why there would have been suggestions for heavier buffer or more spring, but symptoms read like the reciprocating mass is too heavy so I wouldn’t want to add buffer. Also never forget dumb ancillary malfunctions or tolerance stacking in other parts of the system that can impact an already delicate (read: less robustly gassed) rifle: magazine geometry, presentation of magazine, increased drag resultant from alignment issues in the recoil assembly, increased locking/unlocking drag due to alignment issues in the upper assembly, drag on the carrier from the hammer (need more buffer spring for that?).

Your PRS3 should have a spacer to use regular carbine recoil assembly components. Make sure you use that when trying the shorter carbine buffers and springs.

Excellent response - thanks. Definitely certain that it's short stroking as it will not lock back, even without the magazine in, will not load the next round with a mag in, etc. And I have had friends watch it fire and they confirm it's just stopping 2/3rds of the way back. I'm going to try a lighter spring and some carbine buffers/springs with a spacer I ordered.

 

[SupressYourself]

I'm pretty sure you'll have to open that gas port a smidge.

Oh... and "just shoot suppressed all the time" you unwashed heathen.

 

[Constructor]

Pretty sad that he called 2 shops and got the wrong answer then had to go to a forum to get the right one

 

[hlee]

Pretty sad that he called 2 shops and got the wrong answer then had to go to a forum to get the right one

You obviously haven’t stepped into a gun shop in a while. Not getting a correct answer is par for the course…

 

[TheyCallMe64]

I'm pretty sure you'll have to open that gas port a smidge.

Oh... and "just shoot suppressed all the time" you unwashed heathen.

Username checks out

 

[TheOE800]

Pretty sad that he called 2 shops and got the wrong answer then had to go to a forum to get the right one

Sir, I stayed at a holiday inn express.

 

[TheyCallMe64]

UPDATE:
I removed my 5.5 oz rifle length buffer, installed a spacer to shorten it to a carbine length buffer tube system, and had the following results with the adjustable gas block wide open:

-(UNSUPPRESSED) Heavy buffer and spring combination from www.heavybuffers.com (6.4oz buffer) at the recommendation of the guy at Brownells: Ejected, short stroke, failure to lock back or to load the next round.

-(SUPPRESSED) Heavy buffer and spring combination from www.heavybuffers.com (6.4oz buffer) at the recommendation of the guy at Brownells: Ejected, successfully loaded the next round.

-(UNSUPPRESSED) Buffer spring and H1 buffer that came stock with my Daniel Defense DDM4V5. Assuming spring is a standard carbine spring. Ejected, short stroke, failure to lock back or to load the next round.

-(SUPPRESSED) Buffer spring and H1 buffer that came stock with my Daniel Defense DDM4V5. Assuming spring is a standard carbine spring. Ejected, short stroke, failure to lock back or to load the next round.
Surprised this one did not work suppressed.

TLDR, problem persists and was not overcome.

Next steps to try in the coming week:
1) Replace gas rings on bolt
2) Try a JP silent captured buffer spring with the spring kits of varying strengths, and
3) Try my H1 buffer with a Sprinco yellow spring.

If none of these prove satisfactory, and if no other viable solution presents itself on this forum or in my brain, I'm sending the barrel back to Proof for gas hole enlargement.

 

[TheOE800]

Do you have a spare carrier of known provenance laying around? Wonder if your carrier itself is gas inefficient and causing additional problems.

 

[TonyTheTiger]

gas hole enlargement.

I would've already done that myself at this point if I were you.

 

[TheyCallMe64]

Do you have a spare carrier of known provenance laying around? Wonder if your carrier itself is gas inefficient and causing additional problems.

Good idea. Waiting for the email from Midway saying I can come pick up my order for the aforementioned parts, so I'll try that here in a few minutes.

I would've already done that myself at this point if I were you.

The folks at Proof were nice but resistant to the idea until I tried other things, so I listened because I don't want to mess up my warranty.

 

[TheyCallMe64]

Do you have a spare carrier of known provenance laying around? Wonder if your carrier itself is gas inefficient and causing additional problems.

Swapped with my Daniel carrier - no joy.

 

[Cynical]

Have you actually used a pin gauge in the gas port to see if it is in spec? Didn’t happen to me on a proof 6arc, but it happened on a 223 from another highly regarded barrel manufacturer that sells ar15 barrels.

 

[Shifty6BR]

Check your port size..I have a 20" proof +1 it was very finicky cycling...ended up the gas port was on the small side..opened it up a bit and life is good.

Some others have also had the same xp...no bigg once addressed.. the barrels shoot.

 

[cas6969]

Pardon me for saying it, don't be insulted.. but make sure you're not confusing cycling too fast for not cycling enough.

 

[TheyCallMe64]

Have you actually used a pin gauge in the gas port to see if it is in spec? Didn’t happen to me on a proof 6arc, but it happened on a 223 from another highly regarded barrel manufacturer that sells ar15 barrels.

Not yet; have a part time employee who is a machinist and is bringing a set to work in the coming days.

Check your port size..I have a 20" proof +1 it was very finicky cycling...ended up the gas port was on the small side..opened it up a bit and life is good.

Some others have also had the same xp...no bigg once addressed.. the barrels shoot.

As I narrow down options, it seems increasingly likely that this is the issue. It seems like the common denominator. I've read several posts from people on other boards who have said they experienced it too. Not knocking Proof, because even with this issue I'll be buying more from them.

Pardon me for saying it, don't be insulted.. but make sure you're not confusing cycling too fast for not cycling enough.

I've tested with heavier buffers, I've tested with the gas block at various positions from wide open to near closed, I've been able to predictably make it run suppressed when it won't run unsuppressed, and I've confirmed it'll run fine with hotter loads. Pretty certain this isn't it.

 

[GONE BAD]

Your gas tube is to short.
The gas port on my 6ARC 20" with rifle length +1 is only .085 and No AGB and runs like a champ
If your gas tube is to short it will never run no matter how big your gas port is.

 

[TheOE800]

Your gas tube is to short.
The gas port on my 6ARC 20" with rifle length +1 is only .085 and No AGB and runs like a champ
If your gas tube is to short it will never run no matter how big your gas port is.

For OP’s records: my Proof supplied rifle+1 length tube is about 16 1/8” long or almost exactly 410mm end to end. This matches White Oak supplied rifle+1 tubes I have in my possession as well.

 

[Constructor]

Your gas tube is to short.
The gas port on my 6ARC 20" with rifle length +1 is only .085 and No AGB and runs like a champ
If your gas tube is to short it will never run no matter how big your gas port is.

It cycles when suppressed, if the tube was too short it would not.

 

[TheyCallMe64]

UPDATE: I took a bore scope to it today to confirm that the block is aligned correctly.
It is aligned correctly, but I saw what looks like some large chipping/wear uncharacteristic of the low round count on the barrel.

Does this look right?

I've contacted Proof; they verbally told me it was normal but it sure doesn't look normal to me. I will be sending them the photos to confirm.

 

[GONE BAD]

It cycles when suppressed, if the tube was too short it would not.

Not necessarily.
The difference only is about a 1/4" - 3/8" , so barley cycling suppressed and not cycling at all unsuppressed = short gas tube

 

[TheyCallMe64]

Not necessarily.
The difference only is about a 1/4" - 3/8" , so barley cycling suppressed and not cycling at all unsuppressed = short gas tube

It runs fine with factory ammo and powders that burn at a different rate too. I do not believe the gas tube length is the issue. I'm beginning to think the gas hole needs to be enlarged, like it did for the folks in this thread. https://www.snipershide.com/shooting/threads/proof-research-gas-ports-undersized.7129496/

 

[msgriff]

It runs fine with factory ammo and powders that burn at a different rate too. I do not believe the gas tube length is the issue. I'm beginning to think the gas hole needs to be enlarged, like it did for the folks in this thread. https://www.snipershide.com/shooting/threads/proof-research-gas-ports-undersized.7129496/

The gas tube should end in the center of the cam pin cut-out, as shown in this pic (Aero M5 upper).

 

[TheOE800]

UPDATE: I took a bore scope to it today to confirm that the block is aligned correctly.
It is aligned correctly, but I saw what looks like some large chipping/wear uncharacteristic of the low round count on the barrel.

Does this look right?

I've contacted Proof; they verbally told me it was normal but it sure doesn't look normal to me. I will be sending them the photos to confirm.
View attachment 8080561

Eh, gas port erosion has a lot of factors.

 

[TheyCallMe64]

UPDATE 2/21/23

-Installed new gas rings on bolt. Ensured gas block was wide open. Test fired. Failure to load next round; failure to lock back on last round.

-Installed JP Enterprises Silent Capture Spring system. Test fired. Failure to load next round; failure to lock back on last round.

-Installed JP Enterprises reduced power spring (white). Test fired. Failure to load next round; failure to lock back on last round.

-Bore scoped barrel; confirmed that gas block is properly in line with gas hole. **This revealed something new, see below**

At this time, I believe I've exhausted all likely options, and I don't think the Sprinco reduced power spring will yield any wildly better results than the JP reduced power spring.

Therefore, I will pursue opening up the gas hole and report back.

**After scoping the barrel, my gunsmith saw what he labeled "a really concerning problem with your barrel." I've attached the image here. It looks concerning to me, but Proof's reassuring response seems reasonable. Just want to confirm that the "chip" wear doesn't look problematic to y'all.

 

[Maxduty]

When they drill the gas port, small burrs are present in the barrel at the port. the first rounds usually rip them off, so that's not that concerning.

 

[Constructor]

That is normal gas port erosion in a stainless barrel.