Full circumference case bulge, 6ARC

[OREGUN]

Any gas-masters care to weigh in on what’s causing this bulge AHEAD of the case head? Hornady factory (black and match). Happens in about 20% of cases. Suppressed and unsuppressed. 22”, +2 gas.

Gun runs fine, shoots great. Still waiting to hear from manufacturer.

 

[LRRPF52]

That looks like an over-sized chamber to my eyes.

 

[OREGUN]

That looks like an over-sized chamber to my eyes.

And everything ahead of the web is expanding accordingly?

 

[jhoyda]

And everything ahead of the web is expanding accordingly?

I would bet. Measure from the head of the case to the bulge. Now measure the depth of the recess in the bolt. I bet they’re almost the same.

 

[Rocketvapor]

That would be a pretty DEEP bolt head.
Face depth is likely 0.140".
Thin body (ahead of web) is expanding.

 

[jhoyda]

That would be a pretty DEEP bolt head.
Face depth is likely 0.140".
Thin body (ahead of web) is expanding.

Yeah, that makes more sense. Looking at the picture more closely you’re right.

 

[msgriff]

Maybe measure the case and compare to the chamber drawing.
SAAMI 6ARC
Chamber diameter at the 0.200" reference from the bolt face/base - 0.4426" (+0.002")
Chamber diameter at the 1.000" reference from the bolt face/base - 0.4325" (+0.002")

 

[Niles Coyote]

Brainstorming, but my thinking would be either you are getting increased pressures on those 20% or those particular cases didn't form correctly during the brass drawing process and have thinner case walls.

 

[JerkyFreak]

My Lee-Enfield No1MkIII* rifle (circa1919) did the same. It had very generous chamber dimensions...

If you increase the load a bit, it will happen with most of the cases.

 

[Ledzep]

It's a generous chamber. Not going to hurt anything except brass life.

 

[hlee]

I have a Remington 700 in 270 win that does something similar, though less severe. Not really a bulge, per se, but you can see the junction between the case web and the case wall on once-fired brass- where there was no indication of such a junction before firing.

 

[357Max]

@OREGUN - The chamber may well be in spec. Measure the Brass at the .200 line. I ran into the same thing. Turned out it was the Hornady brass undersized at the .200 line. After 3 full power firings it never blew out the bottom to saami. Had the reverse step. I caveat that with the fact I'm using a Wilson FL bushing die which sizes to saami.
I just switched to Lapua, Starline, & Norma for Brass. It wasn't worth culling the +-20% of Hornady that did this especially since the Hornady 6 ARC brass availability & price sucked.

Below is a link where I measured it etc.

Grendel-like Belted Magnum Problem

To follow up on what I was saying with Quick Load or the other internal theoretical ballistics model: Here’s Hodgdon’s published data on the 90gr TNT on top of Benchmark, a compressed load, next to QL: 6.5 Grendel Benchmark 2.200” COL 30.5gr compressed load 90gr TNT 47,000psi It’s one of the...

www.snipershide.com

 

[OREGUN]

Hear me out here. This is what I’m seeing and how I’m thinking about it. I‘m on the other side of the world from the rifle at the moment so no new measurements to be made. However, I measured a fired case at the .2” line and the 1” and measured the bulge which falls at approx. the .250” line from the head.

.200 reference: .436”
1.000 ref: .435”

the bulge: .445”

I’m using consumer grade measuring tools here so I’m not ready to define the quality of the machining based on this alone. Numerous pieces of once fired brass all measure the same. I didn’t measure any brass prior to firing. It looks to me like the chamber is cut within appropriate dimensions. If we pretend that max saami chamber at .200” and .250 are the same (not much taper, I’m okay with this fudge factor, I think) the spec is .4426” (+.002)….for a max chamber size of .4446”. Compared to my measured .445”.

I’m not sure that I’m measuring accurately enough to resolve the .0004” difference. Of course there is also some body taper so at .250”, the diameter should be a tad smaller than the .200” spec.

Is Hornady making their ammo real small to make sure it feeds in every dremel-cut chamber out there?
Is this chamber cut a bit fat (likely so any amateur reloader who has never heard of a small base die can get the job done)?
Is the case web simply not expanding on this first firing but the thin upper case is?
Will one of these cases eventually come apart or be ripped in half by the extractor: best case, jam the gun or worse case, blow my face off?

Im not reloading this brass so I’m ambivalent, to an extent, beyond safety concerns. The rifle makes .5” groups from assorted positions with ease. Kudos to GA Precision for their work in that regard. Still waiting (two weeks now) for a reply from them regarding their thoughts on this particular issue. Not terribly impressed by the customer service at this point.

 

[supercorndogs]

My unfired starline is .438 at the .2 line, and fired is .442-.443 at the .2 line. Sized is .440-.441 at the .2 line. As measured with shitty calipers. It's either 9x or 10x fired. 4x in Rainer um and 5-6x in CMMG.

This is two peices fired from the rainer UM I had to cull because they wouldn't size enough at the base to fit in my CMMG barrel. They measured .445-.446 at the .2 line.

 

[hlee]

If you are not reloading, the gun shoots to your satisfaction, and the only concern regarding the brass is the blown out appearance- stop worrying and shoot the thing. It is VERY unlikely that you will have a case head separation on virgin brass. The brass is going in trash/recycling bin. Shoot more. Worry less.

ETA- I did have a case head separation at a match, on a piece of 6.5 Grendel brass that had been reloaded 4-5 times. (It wasn’t a full separation, but a crack or rip about 40% around the circumference.) The report was a bit “off” and there was more smoke from the ejection port (AR), but the gun continued to cycle, and I’m not 100% certain that the shot wasn’t a hit.

I adjusted my resizing after that, and checked all of my brass for signs of stretching too.

I bet there are s lot of shooters and guns that would see the same thing if they cared to look. But, they’re happily leaving their brass strewn about the range- oblivious to the ugly brass leaving their gun…

 

[bigjake83]

I've been informed by several custom Barrel Smith the Case bulging is due to the soft Hornady Brass. I also saw some slightly bulging cases that come out of my Craddock RTR 14.5" 6 ARC barrel while shooting the 80gr ELD-VT Factory Ammo. The bulg was light and only about 40% of the circumference.

I have some Lapue and Starline Grendel brass that I'm going to resize and see if the issue continues.