Criterion barrel brass pressure signs

[Josh555]

I recent did a build with a criterion pencil 16" mid gas 223w chrome lined. Initial impressions were good, a quick borescope through the bore reviled no obvious defects. It has been shooting factory ammo noticeably better than some of my BA barrels.

The second range day out, I ended up popping several primers causing the FCG to get jammed up. Upon recovering the brass, I found 5 pieces without the primer (out of ~200 rounds), and almost all had ejector swipes. This was winchester/lake city m193. I also tried some pmc x-tac m193 and still got aggressive ejector swipes, but no popped primers (out of 50 rounds). Historically I have found the pmc x-tac to be on the lighter side (chrono 2950 out of a 16", 3120 out of a 20"). I tried this factory ammo in several other know good guns and zero issues with ejector swipes or pressure signs.

I had some really light reloads with virgin starline 556 brass that I used for the first shots in order to start burnishing out the reamer marks in the throat/lands area before making any accuracy assessments. No pressure signs using that ammo. "break in" process and zero pressure signs with that stuff. By "break in" I just mean getting a few hundred round down the barrel before making any accuracy assessments or starting load development.

other info about the new criterion build:
SOLGW BCG
adjustable gas
a5 buffer system w/A5H2, new sprinco green buffer spring

I'm wondering what to do at this point... The only obvious things I can think of is contact criterion or try a larger variety of factory ammo.

 

[bfoosh006]

I would start by, Making sure the chamber and bore are thoroughly clean of any packing / shipping oils.

All my Criterion barrels have come soaked in oil.

Check , with your borescope, the chambers leade area. If possible post a video or pics here.

And your 223 Wylde chamber should be fine with 5.56 NATO ammo... if it is still popping primers , then I wouldcontact Criterion.

 

[Josh555]

I would start by, Making sure the chamber and bore are thoroughly clean of any packing / shipping oils.

Yes I did do this right when I got it during the borescope inspection. I also polished the feed ramps a bit so the brass/bullet doesn't get torn up as much.

 

[msgriff]

Which AGB, how are you adjusting it, and have you re-adjusted since "break-in"?

 

[Josh555]

Which AGB, how are you adjusting it, and have you re-adjusted since "break-in"?

Superlative arms, restrictive mode, yes.
I have about 10 superlative AGB's, I am not the set it and forget it type.

 

[Josh555]

@bfoosh006 at this point the barrel has almost a 1000 rounds through it. About 400 were my light reloads with virgin starline 556 brass/62 hornady fmj.

 

[msgriff]

Superlative arms, restrictive mode, yes.
I have about 10 superlative AGB's, I am not the set it and forget it type.

Are you adjusting based on ejection angle or minimum gas for LRBHO?

 

[Josh555]

@bfoosh006

 

[Josh555]

Are you adjusting based on ejection angle or minimum gas for LRBHO?

Both. I like to see what the minimum setting is to achieve LRBHO on a clean gun, then add gas to get proper ejection (3-4 o'clock). A couple more clicks open for reliability and still good ejection.

 

[msgriff]

Both. I like to see what the minimum setting is to achieve LRBHO on a clean gun, then add gas to get proper ejection (3-4 o'clock). A couple more clicks open for reliability and still good ejection.

How many more clicks or revolutions (4 clicks per revolution) are you opening it up from minimum LRBHO?

 

[Josh555]

How many more clicks or revolutions (4 clicks per revolution) are you opening it up from minimum LRBHO?

4 clicks. With this a5 buffer system, I can just about have the gas all the way open before I observe overgassed ejection.

Of course I reduce gas depending on the silencer I use. I have both flow though and "regular" silencers.

 

[hlee]

You should expect to be able to put any gas block on a barrel and not pop primers or rip rims with common factory ammunition.

 

[msgriff]

4 clicks. With this a5 buffer system, I can just about have the gas all the way open before I observe overgassed ejection.

Of course I reduce gas depending on the silencer I use. I have both flow though and "regular" silencers.

Is your issue happening while running suppressed, and if so, what specific suppressor(s)?

 

[DeathBeforeDismount]

There is no such thing as break in with a chrome lined barrel...so have fun with that.

 

[Josh555]

There is no such thing as break in with a chrome lined barrel...so have fun with that.

Again, not really break in, just "burnishing" out the reamer marks in the throat/lands area.

Similar to what has been mentioned by Molon

see here: https://www.snipershide.com/shooting/threads/criterion-core-barrel-accuracy-evaluation.7096829/

 

[TonyAngel]

The gas block has nothing to do with an over pressure situation occurring in the chamber. Have you checked headspace? The ejector swipes could be caused by a few different things, but before chasing that down, id check the headspace.

Don't tune your rifle based on ejection pattern. There are things other than gas flow that will affect ejection pattern. Tune to reliable lock back on an empty magazine.

 

[Josh555]

The gas block has nothing to do with an over pressure situation occurring in the chamber.

Thanks for confirming this, and no offense @msgriff, but I was starting to question the pertinence of your questions regarding gas block setting/silencer type.

Have you checked headspace? The ejector swipes could be caused by a few different things, but before chasing that down, id check the headspace.

I did not check headspace, but I have been checking the spent brass in a L.E Wilson and Whidden Gunworks case gauge I use for reloading, the spent cases headspace is shorter than 223 rem no-go. I will dig up my headspace gauges, disassemble the bolt, check, and report back.

While I am 99% sure that headspace is within spec, the only thing I can think of with excessive headspace is case-head separation. But even that shouldn't be an issue on the first firing with lake city brass. I did make the mistake one time of buying machine gun fired 7.62x51 brass, and I was getting hard sizing and case-head separation on the first re-load. But that didn't appear to have any effect on whether the loads were over-pressure.

 

[DeathBeforeDismount]

Again, not really break in, just "burnishing" out the reamer marks in the throat/lands area.

Similar to what has been mentioned by Molon

see here: https://www.snipershide.com/shooting/threads/criterion-core-barrel-accuracy-evaluation.7096829/

The chamber is chrome lined too, so not sure how that's going to work. Any imperfections or tooling marks left over, including sharp edges will be covered by the chroming. So unless you plan to shoot enough to wear through that chrome lining (maybe 25-35K rounds of high volume), probably way after the gas port erodes away, Its not happening.

 

[Josh555]

The chamber is chrome lined too, so not sure how that's going to work. Any imperfections or tooling marks left over, including sharp edges will be covered by the chroming. So unless you plan to shoot enough to wear through that chrome lining (maybe 25-35K rounds of high volume), probably way after the gas port erodes away, Its not happening.

The borescope indicates otherwise. Luckily, I bought 2 of these barrels so I can compare a new one against one with ~800 rounds (the one in which this thread was started for).

The left is an uncleaned barrel after ~800 rounds, the right is a new one with the packing oil cleaned out. IMO, this is a clear indication that the sharp edges of the lands are being "burnished" away.

Here is a good video showing what 15k rounds does to a CL barrel:

 

[whatsupdoc]

That is quite a bit of fire cracking for a chrome lined barrel with 800 rounds, are you doing a lot of mag dumps.
Almost looks like rust.

Maybe you should try cleaning the barrel and see.

 

[Josh555]

That is quite a bit of fire cracking for a chrome lined barrel with 800 rounds, are you doing a lot of mag dumps.
Almost looks like rust.

Maybe you should try cleaning the barrel and see.

To be honest, I was thinking the same thing regarding the fire cracking. I didn't express that thought due to my lack of experience with chrome lined barrels. I doubt its rust, I live in a pretty dry climate and the only range days have been good weather.

I have cleaned the barrel 4-5 time since new.

No literal mag dumps, but medium to high cadence training drills on the shot timer. 3 mags in ~10 min followed by a long cool down period before starting a new set of drills. I did one 30 round string from a bench at medium cadence (60-90 sec total) to gauge accuracy of factory ammo compared to my existing ballistic advantage, it was noticeably better. This was done with winchester/lake city '24 headstamp m193. This was done prior to the popped primer incident that sparked this thread.

I'll post some more borescope shots:

1st and 2nd are the cleaned criterion barrel that thread references, the 3rd image is 1.5" from the lands. 4th image is the gas port, 5th is the land opposite the gas port.

My current daily driver/main squeeze is a ballistic advantage 16" pencil 4150 nitrided mid gas 556 nato 7 twist with ~1500-2000 rounds. Not as sure on the round count but at LEAST 1k. Lands appear to be nicely burnished in and some light fire cracking. Firing schedule is no worse than the above mentioned on the criterion. This ballistic advantage barrel has been a good shooter for me and what I expect from it.

 

[MontanaMan]

I've spent half a lifetime working with electroplated chromium & other types of coatings as well...........just not on gun barrels.
And that's a schitty chrome job; the underlying chrome in the areas shown was plated as abnormally nodular/rough.

And the beginnings of the chrome peeling is indicative of poor adhesion.............won't be long until you have some significant coating failure.

I would return that barrel with your photos & get a replacement of a refund & not waste another minute on it.

But I still don't think that accounts for the high pressure, not really sure what that cause could be; your ejector swipes are indicative of unlocking too soon so it's either over gassed or your buffer / spring combo is allowing too quick of a bolt unlock & movement with no delay.

JMHO, YMMV

MM

 

[tucaz]

years ago i had 2 crit barrels (556 and 308) that both had tight chambers and popped primers. i see things haven't changed.

 

[Josh555]

years ago i had 2 crit barrels (556 and 308) that both had tight chambers and popped primers. i see things haven't changed.

 

[Josh555]

I got ahold of criterion and this was their initial response:

I would be happy to have a pre-paid UPS return shipping label sent out to cover the cost of bringing in your complete upper receiver for a detailed inspection and testing. This would allow me to evaluate the barrel in detail but also all of the supporting parts and pieces to see how they are fitting and functioning together. Blown primers are typically the result of improper headspace, loose gas rings, out of spec ammunition, or an improper recoil assembly. If you have loose headspace or gas rings, it is entirely possible that you are experiencing chamber pressure fluctuations and this will result in premature wear of the barrel as it works to contain pressure spikes. If you have any questions, please don't hesitate to contact me directly.

I'm having a hard time understanding how loose gas rings or an improper recoil assembly has anything to do with chamber pressure. Peak chamber pressure occurs within the first few inches of the barrel, long before the bullet passes over the gas port.

 

[Cascade Hemi]

I got ahold of criterion and this was their initial response:



I'm having a hard time understanding how loose gas rings or an improper recoil assembly has anything to do with chamber pressure. Peak chamber pressure occurs within the first few inches of the barrel, long before the bullet passes over the gas port.

Their response is pretty retarded and that's a rough looking 800 rounds of wear.

Excessive gas can cause early unlocking, which can cause ejector swipes and blown primers. So can an improperly made barrel. The pictures don't lead me to think the issue is gas related.

Loose gas rings generally causes less gas pressure in the BCG. Tight rings cause more gas pressure in the BCG.

 

[Josh555]

Minimum pressure at gas port to cycle a stock AR - AR15.COM

Firearm Discussion and Resources from AR-15, AK-47, Handguns and more! Buy, Sell, and Trade your Firearms and Gear.

www.ar15.com

 

[Josh555]

I should have shared this earlier, but this is clearly overpressure

 

[tucaz]

I got ahold of criterion and this was their initial response:



I'm having a hard time understanding how loose gas rings or an improper recoil assembly has anything to do with chamber pressure. Peak chamber pressure occurs within the first few inches of the barrel, long before the bullet passes over the gas port.

i'm not expert by far but have 30 years of shooting ar15's and have worn out alot of gas rings. never once did it over pressure, it just fails to cycle fully.

that answer is garbage and he was cat little boxing....covering up the shit in hopes no one sees it.