PA10 (PSA Version of AR10/LR308) Rupturing Steel-Cased Ammo and Piercing Primers

[44 AMP]

Hi currancchs,

I absolutely have to agree with Slamfire about this..

Clearly that ammunition is too hot for that barrel. That is just the bottom line, whatever bullet, powder, case, the combination or even just one element is too hot for your barrel.

Here's a question, is it too hot because its too hot, or is the timing of your rifle making it too hot, or perhaps both, with one compounding the effect of the other?

Here's something to try, (if you are willing to take the risk of continued shooting) for information if nothing else, turn your gas system OFF, and fire a few rounds of the ammo in question. (I am not familiar with your specific parts, but an adjustable gas system should include an "OFF" position".

Shooting the rifle in manual mode removes all factors relating to semi auto timing. That should allow you to find out if the timing is in any way a factor.

It is possible that while "in spec" your Frankengun might require special care and feeding. And I use "Frankengun" in the sense used in the 1931 classic. To quote Colin Clive (Victor Frankenstein) "that body is not dead. It has never lived. I made it, from parts..." I don't find it a derogatory term, and think its cooler than "parts gun". Made from parts by a "mad doctor" (us) = Frankengun. Starting with a gun and replacing stock with custom parts is not Frankensteining a gun, its 6 million dollar man /Robocop / cyborg "ing" a gun. In my not so humble opinion.

Also, spend a couple bucks and get some proper gauges. There is a firing pin protrusion gauge for the M16, min/max. I'm sure something like that exists for the AR10 class rifles. Its a better indicator than calipers because it gives you instant feedback.

I've rebuilt M16/A1s for the Army back in the 70s. I've built a couple AR-15 variants in the 80s. Have shot a friend's AR-10 variants (from 3 different makers) fairly extensively. I know a little bit about shop work, I just don't do it anymore, as other things have a greater interest for me these days.

There are lots of things in your build that while individually fine, might be "stacking tolerances" until things are (obviously) NOT fine.

Semi auto operation is a tightwire balancing act. All the factors of gun AND ammo have to work in harmony or its a fail. The more complex the system, the more crucial this becomes, and a DI gas operated system is almost as complex as it gets.

Good Luck!

[James K]

"Pierced" primers have one cause - pressure forcing the primer metal back into the firing pin hole in the bolt (and leaving the little "disc" there, a point for future reference). They are usually the result of a light firing pin/hammer spring.

Jim

[44 AMP]

Pierced" primers have one cause...

Too high pressure is the most common cause, I would agree. But, pierced primers can also be caused by the less common mechanical flaw of a firing pin with too long a protrusion. And that happens at any pressure, because its a flaw of the gun, not the ammo.

[40CalGuy]

you need to get a go/no go headspace gauge on that thing. that primer hit looks excessively deep

[Jimro]

you need to get a go/no go headspace gauge on that thing. that primer hit looks excessively deep

Headspace gauges only measure from the bolt face to the shoulder datum point in the chamber, not firing pin protrusion. Excess headspace shows up as brass stretch or brass cracking in the body and shallower firing pin strikes.

Firing pin protrusion is a different measurement than headspace and if the OPs measurements of firing pin protrusion were accurate it isn't a protrusion problem. Key word there is "if."

Never hurts to verify headspace though.

Jimro

[currancchs]

Thank you all for the continued discussion, it is quite informative. I apologize for my lack of response lately, I closed on a house on Friday and have not had access to a computer/been busy moving this weekend. Unfortunately, figuring out this rifle may have to wait until moving-related tasks are completed, but I am certain that I will eventually get to the bottom of this and will update this thread when I do.

Regarding the light primer strikes as a possible cause of cratering/pierced primers, I am running an ALG ACT trigger with the lighter (4.5lbs. trigger pull) spring so could certainly try swapping that out for the stronger (standard strength) one that also came with the trigger to rule out light primer strikes as being a contributing factor. Didn't think of that one before.

I had also come across another thread that had implicated a NiB BCG as the cause of timing issues. Apparently that poster had tried to slow down the BCG using heavy buffers with only limited success and eventually found that using a standard phosphate BCG did more to slow down the movement than the heaviest available buffer weight...

44 AMP
Turning the gas off completely, making the rifle essentially into a bolt action, to determine whether I have a timing or chamber issue sounds like a great idea! I will try this as soon as I can, but that, unfortunately, may not be for a couple weeks.

Thanks again everybody!

[currancchs]

40CalGuy
Thanks for the tip. That's what I had originally thought as well, so I did pick up Go/No Go headspace gauges and checked, but everything checked out.

[stagpanther]

What I *think* is happening is that your rifle is experiencing high pressure symptoms in combination between a tight chamber and temp sensitive powder. The pierced primer is actually a good sign because it means the pressure spike happened while the bolt was still fully in battery, where a popped primer would mean you got a pressure spike while the bolt was out of batter (a common symptom when people shoot surplus 5.56 ammo through a 223 chamber and the ball powder produces a secondary pressure spike which translates back into the chamber just as the bolt is unlocking).

When ball powder is difficult to ignite, the initial pressure from the primer can push the bullet into the lede where it gets stuck until the powder "catches up" and you see a higher than normal pressure spike, one of the reasons why so many people recommend magnum primers for ball powders.

I'm with JImro on this--while I think it's possible that all the other things mentioned may or may not be issues--my suspicions lie with an over-pressure occuring as a result of the cartridge not conforming to the chamber properly--could be the bullet forced back--the case not headspacing on the shoulder datum of the chamber etc--but the mere fact the cases were ejected tells me it's unlikely it was solely a primer or powder failure while the cartridge was fully chambered normally. I also think proper bolt lock-up is a leading contender, whether due to improper headspacing or something else.

PSA warns all over their web store that their components only play well with their own parts--and with good reason. While I've had good results with their AR 15 stuff--their PA 10 stuff is sometimes unpredictable and challenging to get to play well with other's parts.

[currancchs]

Just wanted to provide an update on my situation; I've been extremely busy these last 5 months or so and had to put this project down for a bit. Thank you all again for your comments throughout this process.

Last month, I started thinking about this issue again and wound up purchasing a new barrel from Black Hole Weaponry. The new barrel is a 20'' 3-groove polygonally-rifled barrel with a rifle-length gas system. I got this barrel not so much because of the extra 2'' or because of the polygonal rifling (although I do like that they seem to be easier to clean), but because, in hindsight, I realized that a rifle-length gas system would probably be more reliable, easier on the components, and provide better timing, especially of extraction, as this was what the rifle was originally designed around. I went with Black Hole because they offered

It's been 5 weeks since I placed my order and I'm still waiting for the barrel to arrive (estimate was 6-12 weeks). I will update this thread with my results once I've had a chance to install the barrel and get back out to the range.

[Ignition Override]

If pierced primers sometimes equate to 'popped primers', Tula ammo contributed to both situations in my pair of nice Yugo M59 SKS. One firing pin was blown out the rear of the bolt!

I'm not trying to equate an SKS to the OP's rifle. This should be obvious, but the common link is Tula ammo in centerfire rifles.

Murray's Gunsmithing in Bowie TX permanently 'cures' any SKS by a little chamber-reaming. His theories seem to be that certain foreign ammo, possibly combined with some non-standard chamber leades are the issue.
Some SKS were manufactured with too little Leade 'Free space' for the bullet to leave the case before excess pressure inside the case ruptures the primer, if I remember correctly.

[rickyrick]

Here ya go:
I've had problems with every caliber of steel cased ammunition in every gun I've used it in. Some better than others.

Bottom line, this is March 2017, there's no reason to be shooting steel cased ammunition. Just my opinion.

[currancchs]

Just another update, the new barrel (Black Hole Weaponry) has still not arrived. It's been about 13 and a half weeks at this point (Original estimate of 8-12 weeks IIRC).

Customer service has indicated that their barrel extension manufacturer is out of 308 barrel extensions and their customer service reps have no idea when they will be able to obtain more, although there seem to be 308 barrel extensions available on Brownells and MidwayUSA... Their customer service reps are pleasant and easily reached at least though and, based on what others say about their barrels, it should be a good barrel when it does arrive, especially for the price...

As to RickyRick's comment about it being 2017 and therefore no need to shoot steel-cased ammo, yeah, I'm cheap, although I do agree that I'd probably save myself some aggravation by buying better ammo, but what fun would that be .

I've shot TULA extensively before though and always had great luck with it. I've put thousands of rounds of that stuff through an AR15 I built a few years ago and have had no real issues. For half the price of brass-cased, I buy enough brass to have on hand to reload should there be another shortage and then shoot steel ($4.50 per box of 20 (TULA) at my local Walmart and always in stock) pretty much exclusively.

I figure that, even if I do wear out a barrel early, that I'll have saved more than enough to buy a new barrel with the difference. I also don't like the idea of having a rifle that's picky about ammo, in case the selection is more limited in the future.

In this particular case though, I made the mistake of buying a 1000 round box of 308 TULA without buying a smaller batch to test with and have no other 308 to put it through, so I'm kind of invested at this point in making the rifle work with it. Lastly, the rifle is showing signs of over-pressure with quality brass too, just not to the same extent.

IgnitionOverride - Thanks for the comment, I was thinking about having my chamber checked (I did check headspace myself and it was fine) and/or reamed out a bit on my old barrel, but didn't want to sink more money into my Palmetto State barrel (had already had it serviced once by ADCO due to a sheared barrel extension pin, long story) and had changed my mind on barrel length/gas system length since purchasing that barrel in any case (old barrel was 18'' midlength, new is 20'' rifle length).

[Metal god]

I guess I'm going to need someone to explain how a tight chamber increases pressure ??? The only spot in the chamber I can think of that may cause a pressure issue would be a smaller then spec or tight neck area . This would not allow the case neck to expand enough to let the bullet freely release from the case .

Has anyone considered the bore diameter it self is out of spec . Does the OP have the ability to remove the barrel and slug the bore or cast the chamber , lead and a few inches of the bore . This will allow you to measure these areas and see if anything is out of spec . http://www.brownells.com/gunsmith-to...y-prod384.aspx

[currancchs]

Hi Metal god,

OP here, thanks for the input. The barrel is already removed and sitting on my workbench, no problem there. I've never cast a chamber before, or slugged a bore for that matter, but I'm sure that I could figure it out (p.s. thanks for the idea/link!)

RE: Chamber reaming - I'm no gunsmith and my theory is probably wrong, but I had assumed that reaming the chamber a bit would allow the casing to expand slightly more, thus increasing case volume the instant after firing and reducing pressure. Ignition Override's mention of chamber reaming to increase the free space in front of the bullet, allowing it to get up a bit more speed before contacting the lands/grooves also made sense to me (I equate this, maybe incorrectly, to getting a bit of a running start before pulling over the hump lots of people have between their driveway and garage floor v. leaving no space and trying to get over that same hump).

To be honest though, I've put this project on the backburner until the new barrel arrives. I wound up taking on the task of rebuilding three separate motorcycles this winter and am just finishing up the last two with some odds and ends and also just recently became a homeowner, so lots of small projects there too to keep me busy. If the new barrel fixes things though, I'm sure that my curiosity will get the better of me and I'll try your suggestion of casting the chamber/lead/first few inches of bore then and will definitely report back as I appreciate all of the help and wouldn't want to leave somebody who stumbles across this post with similar issues in the dark as to the final resolution/root cause.

[currancchs]

So, I finally got the new barrel in. I checked headspace before installing it and the barrel/bolt combo (black hole weaponry barrel, aero precision NiB bolt) could rotate into partial lockup on the NO GO gauge, but could not rotate on a field gauge. The manufacturer indicated that complaints of improper headspacing seem to be most common where aero precision bolts are used. I might get a JP bolt with the smaller diameter firing pin in the future, so just installed the barrel despite the headspace appearing to be slightly long for new components.

I went out to the range yesterday and put about 100 rounds through the new barrel without significant issue. Although I did have one stovepipe and some light strikes on steel-cased (Tula) ammo, I chalk these issues up to using a 3 lbs. hammer spring and not having played around with the adjustable gas block much yet (I initially set it to 7 turns out (max 12 or so) and left it there since functioning well). There were no signs of overpressure and no difficulty in extraction. Ejection angle was 2-3 o'clock. The cases had no ejector swipes and primers were not flattened/cratered/pierced. I had installed a new firing pin before re-assembling the rifle since the old one had been subjected to some abuse, although it looked fine and I am keeping it as a spare.

The barrel itself is more accurate than I am, but I only shot at 25 and 50 yards, so not really a great test of the barrel's potential. I'll have the opportunity to shoot out to 600 yards in the next few weeks though and should be able to see what it can really do at that range.

In light of my issues, I'd probably recommend staying away from Palmetto State Armory 308 barrels, especially if you are interested in shooting steel-cased ammo, although their PSA10 upper/lower and parts kit seems of reasonable quality for the money and are compatible with DPMS LR-308 low profile (0.150'' tang) barrels, bolts, and most other parts (they sell a parts kit containing all proprietary parts, i.e. the mag release and front and rear takedown pins, for about $20 IIRC).

If I ever get around to casting the chamber of the old barrel and taking measurements, I will post a reply to this thread with my findings.

I hope that this information is helpful to someone else who might come across this thread with similar issues.

Thank you everybody who chimed in for your help!

Picture of finished rifle attached.



p.s. scope is too far forward for my liking in the picture, moved it back once at range (I mount red dot/holographic sights as far forward on the receiver as possible and mounted this scope the same without thinking).

[44 AMP]

Good to hear a different barrel solved your problems.

I re-read the thread, to catch up, and something occurred to me. A possibility, not a certainty.

Case neck thickness. If your chamber is "tight" (on the min end of the spec), and a batch of cases has thick necks, (because of manufacturing tolerances or perhaps, because of an applied coating??) there might be enough clearance for the round to chamber normally, but not enough for the case neck to expand enough to release the bullet easily, and THAT WILL drive pressures UP!

It might be that while the problem barrel is in spec, and the ammo is in spec (for outside dimensions) the combination of the two is not allowing free release of the bullet, and raising pressure. AND it is a problem that will only show up when the ammo is just enough out of spec (neck too thick) and so might not (and probably wouldn't) show up with a different brand, or maybe even a different Lot# of the same ammo.

[stagpanther]

I've installed numerous BHW barrels on both AR15's and AR 10's; I've always found their barrels to be consistently sub MOA shooters. However, I've also found their extensions frequently to be slightly loose fitting in many manufacturer's uppers--this requires a bit of extra care on the install in my experience since even a slight out-of-true alignment to the bolt can result in nagging issues over time.

[currancchs]

Thanks for your thoughts 44 AMP, sounds plausible to me.

Stagpanther - I appreciate the insight re: BHW barrels. Luckily that was not the case for me here, the barrel extension was nice and snug in the PA10 receiver, although I did have to shim the barrel nut by 0.002'' to get the gas tube notches into alignment within the recommended torque spec (30-70 ft-lbs., mine sits at 40 ft-lbs. now, was aligned at 25 ft-lbs. prior to shimming, barrel nut came with Midwest Industries FF handguard).