Case Bulge

[KC_Joe]

Several weeks ago I was at the range running some S&B fmj. While my son was shooting, I was picking up brass and noticed the piece in the photo......all rounds fired that day functioned as they should except 1 ( which didn't lock the bolt back on an empty mag), and I'm guessing this round was that one.

Posted this pic online and received many responses telling me it was an out of battery fire.....with an equal number saying it was something else. Then got a couple responses from a person who seemed knowledgeable, and after some inspection of the rifle, bolt, etc, I've chalked this up to a fluke hot round from the factory.

That said, wanted this group's thoughts.......since then, no additional issues.

Joe

[Klem]

Joe,

Are these hand-loads or factory ammo?

Do any of the other cases show any symptoms, even lesser bulges down at the web?

[KC_Joe]

Klem.....this was factory ammo. In 99 other rounds of this ammo, no issues at all.

[Klem]

Joe,

OK, that eliminates all the usual suspects related to hand-loading.

From the photo it looks like an OOB or out-of-battery firing. The web or solid area of the case appears to be extruded (no chamber support), while the rest of the case was supported by the chamber, so it was almost in and closed.

Why the round went off OOB could be due to a number of reasons: an oversensitive primer, or a proud primer that was not flush or recessed with the pocket, or debris on the bolt face, or loading into a scorching hot chamber and it cooks off, or a BCG without the cam pin.

[lazyengineer]

I'm not aware of an OOB that can happen in a rifle without case-rupture. Grendel is a funny animal and I'm still learning things, but my own bias is unsupported brass in an unlocked bolt isn't holding 52,000 PSI. But to other's point, that is one weird looking failure, that certainly looks like the case expanded in places that normally should have barrel there. Is there such thing as a partial OOB? Premature bolt opening while still under some pressure, but not the full 52,000 PSI? I've recently gotten into annealing and Grendel is tricky because it's so short. Hope I didn't mess that up in fact, because if I did, a failure mode will look not so different from that one, I suspect...

I will say, my opinion of S&B metalurgical QC is not high. I've had more weird experiences and failures with S&B than any other brand. I've seen 6.5CM factory brass rip all the way down to the case head - multiple times. When no other brass did that or complained at all in that same gun. And I've had their primers punch holes the diameter of my firing pin at times in my creedmoor. When no other brass does that. Not just a piecing, but a full punch, with the blunt flying back into the firing pin channel, and after a few build up in there, locking up the firing pin of the gun. All other primers worked fine.

[LRRPF52]

Several weeks ago I was at the range running some S&B fmj. While my son was shooting, I was picking up brass and noticed the piece in the photo......all rounds fired that day functioned as they should except 1 ( which didn't lock the bolt back on an empty mag), and I'm guessing this round was that one.

Posted this pic online and received many responses telling me it was an out of battery fire.....with an equal number saying it was something else. Then got a couple responses from a person who seemed knowledgeable, and after some inspection of the rifle, bolt, etc, I've chalked this up to a fluke hot round from the factory.

That said, wanted this group's thoughts.......since then, no additional issues.

Joe

What barrel length and gas system length do you have?

Do you know your gas port diameter?

That conical bulge is weird. It would be interesting to see that piece of brass sectioned.

[KC_Joe]

18" PSA with rifle-length gas. Not sure port diameter.

[muvef]

I had the same or similar happen. I was a full grain plus over max with AR Comp (still not sure how). It did eject and cycle just fine. Also, I would say you are over gassed.CE4VZ4o.jpg

FYU9g5q.jpg

[lazyengineer]

I had the same or similar happen. I was a full grain plus over max with AR Comp (still not sure how). It did eject and cycle just fine. Also, I would say you are over gassed.CE4VZ4o.jpg

FYU9g5q.jpg

I have never been able to figure out why this is such a distinctly 6.5 Grendel phenomenae. Overgassed 5.56 brass doesn't do this, even at 10,000 psi higher pressure. Nor does an overgassed AR10 (that I know of). I used to think it was maybe brand particular, but while some seem to do so faster than others; all brands will do this in Grendel if you try hard enough. It's a good starting guess that this would be OP's issue, though so odd that only one casing of the factory did this - and did it to a rather exaggerated degree; while the rest all came out completely unscathed.

I do know I basically never experience this, and some of my loads are arguably pretty hot. Hot enough I'll at times get swipes which usually means over-gassed, but I don't get this. Normally I'm running Hornady brass in a PSA or Alexander or SAMMI chamber. with one recent box of reloads, I even got a little ejector extrusion mark, which means I was WAY over pressure on that one. At least I was shooting 800 yards and got the benefit I suppose, but I'll be backing that off. None of that brass did this.

Yet this is a common challenge. I haven't been able to figure it out. Just being overgassed alone isn't an automatic ,but it seems like those that get this, tend to be overgassed. Is the Grendel bullet going so slow there's still pressure in there and the bolt is unlocked and starting to move back, from the overgas? Is that it?

[grayfox]

I have an idea, maybe it is based upon the relative diameters of the 2 cases, 556 and grendel. Even at the lower pressures of grendel, could it be that the bigger diameter makes the case less able to restrain the internal pressures? especially if they are over the Saami max, so say, 60 ksi for both internal cases, but higher force due to larger internal surface area... I'm thinking psi, relative to the force against that larger surface, larger diameter of the grendel case... more bulging to show as a result. Not an engineer but is that perhaps hoop stress? IDK.

[Klem]

Lazy.

Yes, I've had Muvef's situation in 223. Hot hand-loads extruded the web into the bolt face, to the point the spent case rims could not fit into a Lyman Rifle gauge, even after full length sizing. I spun them in a drill press and held a file against the rims until the whole case fit again.

In Joe's case maybe the web extruded to the shape of the bolt face, and as it unlocked and was dragged out of the barrel, the pressure was dropping but still enough to cause that expanded effect on the thinner walls above, but not enough to rupture.

If it was early unlocking then all of the cases would look the same. Maybe this one case was unusually hot for some reason.

[LR1955]

Guys:

This exact same thing came up maybe two years ago. I think there was two separate threads on it over the years. Someone can search for it. It was something like Belted Grendel or Grendel Belted Magnum. Can't remember what conclusions were drawn but I do believe the recommendations did solve the problem.

Not saying to not talk about it now. Just that I believe a solution was found on an older thread.

LR-55

[LRRPF52]

Happens with plenty of other cartridges and actions:

[dammitman]

ive seen factory 30-06 do this all the time not those little fatties from two pics up though,,,,thats weird

[Klem]

Also happens with .22LR on full auto due to bolt bounce.