224 Valk Overpressure: Rifle or Ammo issue?

[Neurotic]

Long story short, in a newly assembled upper I'm seeing over-pressurization signs (and a jammed casing) with Hornady Match (88 eldm) ammunition. I'm not certain where to go and would appreciate any guidance.

More details:
I just reassembled this upper with a new 224 Valkyrie barrel, BCG, adjustable gas block, gas tube and muzzle brake. The bolt and barrel will accept a GO headspace gage, and not accept a NO GO gage.

When firing, the rifle would short cycle. It would eject the spent casing, but not strip the next round or lock back on an empty magazine. I fired a total of 25 rounds and didn't realized I had a problem until the last one jammed the casing in the chamber. I had to remove the casing by pushing it through the bore once cool.

The spent casings show cratered and pierced primers as well as ejector and extractor marks. I thought this was overly loaded ammunition, but realized the rounds came from two manufacturing lots. I'm wondering how likely two lots of hot ammunition would be, versus some other rifle issue? And if a rifle issue, what would cause this aside from headspace?

I was able to find some Federal ammunition, and planned to test with it. Although I'm not certain this is a good idea.

Build details:
- Criterion 22" barrel with rifle length gas
- APOC Armory branded BCG (Toolcraft rebrand)
- Wojtek gas block (was fully open)
- CMMG gas tube (does not appear obstructed)
- Ultradyne Pulse brake
- ASC 6.8 magazines

Thanks.

 

[ormandj]

Chamber/throat, ammo, the fact it's 224V... that's where I'd start. Do you have an OAL gauge or a case you can modify to make one? If you're jammed into the lands that could case a nasty pressure spike. That said, a quick search of these issues leads to a lot of threads with a ton of people having this issue with 224V, a lot ammunition related, a lot chamber/throat related. Good luck, I have 0 experience with that platform, but that's where I'd start if I was you. Bad lots of ammunition do happen, but I also wouldn't be quick to test that theory until you'd removed the possibility of having a short throat.

 

[Neurotic]

I'm not a reloader, so I don't have tools to measure the throat. If the bullet was jammed into the lands would witness marks be left on a chambered bullet?

 

[ormandj]

I'm not a reloader, so I don't have tools to measure the throat. If the bullet was jammed into the lands would witness marks be left on a chambered bullet?

Try painting one with black sharpie then chambering. That might work.

 

[JbBooks]

I would definitely check the chamber before pointing fingers at ammo, I’ve been down the 224V rabbit hole and still hanging out in it, my earlier builds had the same issues with over pressure, stuck casings, and shot like shit, I do know when it first hit the market there were a lot of bad chamberings, even with good barrel makers, so on the off chance you got an older barrel, that may be your issue, since I’ve been using newer chambered barrels, I haven’t had an issue and they shoot tiny little groups, even with factory ammo.

 

[Neurotic]

No marks with sharpie.

The barrel appears to have a date code for August of last year. I'll try to give Criterion a call tomorrow. It shot pretty decently considering it wasn't cycling and I was less than enthused....

 

[Neurotic]

Hornady wants to see the spent casings and unfired ammunition.

Criterion thinks it's either an ammunition issue or the system was over-gassed (AGB too open, not enough dwell time). I'm a bit confused by this assertion, as the marks seem to indicate excessive pressure in the chamber not excessive force trying to extract the casing. I can fully close the AGB fully and test with the Hornady and Federal ammunition.

 

[ormandj]

Hornady wants to see the spent casings and unfired ammunition.

Criterion thinks it's either an ammunition issue or the system was over-gassed (AGB too open, not enough dwell time). I'm a bit confused by this assertion, as the marks seem to indicate excessive pressure in the chamber not excessive force trying to extract the casing. I can fully close the AGB fully and test with the Hornady and Federal ammunition.

Hornady will definitely want to check on that, so good on that front. Regarding over-gassing, I'm not sure how that'd cause short-stroking that you indicated. Violent cycling, sure, which can lead to issues in operation, but not short-stroking which is absolute proof the rifle isn't over-gassed. Just be very careful if you go fire again, like mounted in a vise using a remote trigger and standing behind a blast shield kind of careful, hah. I'm sure it's not that serious, but better safe than sorry. You mentioned you're not a reloader so don't think you have all the tooling you'd need to measure everything, so best to let Hornady/Criterion tell you what to do. I just have a bit of a WTF re: them telling you over-gassed when you've directly said it short-stroked. That scares me.

 

[hlee]

Over gassed can appear to be short stroking if the carrier is moving so fast that the mag can’t feed the next round before the carrier zooms past.

Those are definitely 2 pierced primers, but the primers don’t look especially flattened. Gas guns are hard on brass and can leave “pressure marks” that are false indicators, especially when over gassed.

That said, I had a similar experience with a 224 predator build. What buffer are you running? If it is too heavy, you can get short stroking even with the gas fully open. I’d recommend a standard weight buffer, h1 at the heaviest. Turn the gas system off, then shoot one. Look at the brass. My guess is that it will appear much less abused. Now, open the gas block by a couple of clicks, load one round in the mag and fire. Continue until the bolt locks back, or the gas block is fully open. If it never locks back, you probably need to get a lighter buffer. If it does lock back, go 2 clicks past that point for reliability.

 

[Neurotic]

In fairness, Criterion did offer to take a look at the upper if nothing panned out with Hornady or gas block adjustments.

It doesn't feel like it's cycling overly fast; sort of feels like the BCG is lazily slapping back. It has an odd recoil sensation, but not more harsh than I'm accustomed too.

As mentioned, I'm going to try with gas off to inspect the case without the variable of cycling. If there are no pressure signs, then slowly open the gas system. The guy from Criterion didn't like this approach and recommended just setting it half open.

The lower has a standard rifle buffer, so heavier than most carbine buffers but with the softer spring. The lower is unchanged from when the upper had a 20", .223 barrel with a rifle length gas system and a partially closed AGB. So, I'd expect this barrel would be slightly more over-gassed than that, but not radically so.

Thanks.

 

[hlee]

I'll warn you that with the gas fully off, you may need a non-marring mallet to tap on the charging handle, or a wide tipped flat tip screw driver to wedge open the BCG (through the mag well). In other words, without some gas to break things free, you may find the BCG difficult to open. Half open may be excessive to start, but fully closed may bring along its own baggage.

 

[Neurotic]

Thanks. I didn't think of that.

Random thought, could the gas block's internal volume at full open cause under-gassing issues? That could drop the pressure signal to the BCG and delay opening.

 

[XLR308]

If your port pressure is to high and the carrier is trying to extract the case it will give signs like your seeing.
The radius of all your primers look nice and round but you have extractor marks and several of the primers have the firing pin indent forced back out.

 

[Neurotic]

Slight update...

In packing up to test, I realized the casings were only from one Hornady lot; the two lots have different primer crimping (? I think that's what it's called). So I dug around my range bag and found two casings from the other lot. These still had ejector and extractor marks, but the primers look fine. So maybe there are two issues, and one lot is doing something weird causing the cratered and pierced primers. The picture shows casings from the two lots.

I also noticed the casing that was jammed has a black ring with a divot through it. I have no idea what this means.

Thanks.

 

[ormandj]

Slight update...

In packing up to test, I realized the casings were only from one Hornady lot; the two lots have different primer crimping (? I think that's what it's called). So I dug around my range bag and found two casings from the other lot. These still had ejector and extractor marks, but the primers look fine. So maybe there are two issues, and one lot is doing something weird causing the cratered and pierced primers. The picture shows casings from the two lots.

I also noticed the casing that was jammed has a black ring with a divot through it. I have no idea what this means.

Thanks.

Do you have a bore scope or some way to look inside your chamber? That could be from a chamber imperfection. The dent could be from a brass burr or something stuck in the chamber, as well. See if you can look in there and spot anything with a light if you don't have a bore scope. If it was lower down near the case head it might be stretching due to excessive headspace, but I would think that's too high (keep in mind I'm not a 224V shooter, so don't know what the brass/design is like.) The ammunition could also have issues, but I can't see how that would cause a dent like that.

 

[bigjake83]

I personally think the chamber was cut a bit shallow and it's increasing the pressure, did you check headspace?? That will tell you a lot. Take the offer and send in the complete upper to Criterion.

 

[Neurotic]

Headspace is fine per my Clymer gauges...

I don't have a borescope, but may look for one now.

Update from a quick test today:

I started with the gas block 1/4 open and ran Federal 90gr and the two Hornady lots, and increasingly opened the AGB
- FGM 90gr: locked back with AGB at 3/4 open, ejected casings at 3/8 open, primers look good, some ejector marks.
- Hornady older lot: never fully cycled, did manage to cycle enough to eject casings at 3/8 open, no primer irregularities, some ejector marks.
- Hornady newer lot: cratered and pierced primers with AGB between 1/4 and 1/2 open, did not cycle enough to eject, resulted in noticeable smoke wafting from the chamber when manually cycling the BCG, ejector and extractor marks.

So, it seems the upper doesn't like the Hornady loading, with one being substantially worse.

 

[Neurotic]

This should be typical casings from today, in the following order:
1. Federal 90gr
2. Hornady 88gr old lot
2. Hornady 88gr new lot

 

[DarrinW]

I have a CMMG 224V and had issues with Hornady cycling also. I chronoed them running at 2880 out of a 24" barrel so they seem pretty hot. The federals always run fine though.

 

[Neurotic]

So, would that be too much chamber pressure to unlock the bolt and extract?

Or something like a fast piwder burn, with lots of initial pressure, but not enough pressure at the port? So, a larger gas port may be necessary.

 

[Neurotic]

Well, the Hornady lot that had primer issues was found to be overpressure. Hornady is replacing the ammunition.

The upper is on its way to Criterion for an inspection. They claim the gas port spec is 0.081", but I measured mine with plug gages somewhere under 0.080" and over 0.079". I feel like the gas port spec may be a marginal, and the slight undersizing is causing cycling issues.

 

[Islander]

Criterion should do right by you, they stand behind their products. Might want to ask them about throat angle. When the 223 Wilde first came out it was all the rage. Only some bullets had different ogives and there were some pressure issues like you describe. Blown primers, stuck cases, etc. I had the throat angle recut in my 3 gun rifle and it solved the problems.

 

[357Max]

- APOC Armory branded BCG (Toolcraft rebrand)

Check firing pin protrusion. If it's to much it will cause your pierced primer issue. Below is a video that explains better.


On another note: Hornady QC is complete shit lately.
I just built a .224 and ran the first 40 rounds of the Hornady 88ELDM through it. Had some short stroking, but no pierced primers. Mine is an 18" with +1" rifle gas so I was kind of expecting to have to lighten the buffer.
Look at this pic. Both Hornady "Match" 88 ELDM the primers look like ass on 1 box. They are rusted & staked vs silver & re-loadable.
Not even going to shoot the rusty ones & both boxes came in same order....WTF Hornady!

 

[Neurotic]

Yeah, I've heard Criterion has good CS. Although, I'm a bit concerned since in speaking with them, they believed almost all 224Valk issues are ammunition related and there were no out of spec reamers (that was an internet rumor) so they didn't want to discuss chamber geometry issues.

I measured firing pin protrusion as best I could (not the best technique), and everything seemed fine with two different pins. I also gaged the firing pin hole and it was in spec.

Of the two Hornady lots I had, the normal primer ones were overpressure and would damage the primer the "staked" primer ones didn't do anything weird, but would cycle the rifle.

Hopefully the gas port gets opened and feeding it new ammunition fixes these issues.