357 Case Head Separation

[azdover]

A long post but I'm trying to get as much info out there for my questions.

I had a case head separation today with a 357 Magnum handload in my Big Boy Steel.
- 158 gr Xtreme Plated SWC
- Twice fired Federal brass
- Federal 200 Small Pistol Primers
- OAL 1.590'
- Medium taper crimper
- 7.3 gr Power Pistol not CFE-P

I was using Xtreme's load data for their other 158 gr plated bullets for reference since they didn't specifically list a load for their SWC. Their other bullets listed 7.6-7.7 grs max with a muzzle velocity just shy of 1300 fps and max pressure of about 29,000-30,000 psi although they don't list a barrel length. I figured 7.3 grs was safely below the max. I had worked up from 6.4 grs to 7.3 grs in both revolvers and my rifle and didn't see any problems of overpressure - no flattened or cratered primers, no sticky cases during extraction. I was getting about 1000 fps from my 5 1/2" and a 7 1/2" revolvers and about 1300 fps from the 17 1/2' barrel on the Big Boy, both with single digit SDs.

I had already fired about 15 rounds through the rifle when this happened and was recording data with a Garmin Xero C1 Pro. It showed the shot at 1319 fps. There was no muss or fuss - the only indication I got the case head had separated was a FTF for the next round. When I turned the rifle on its side to clear the next round, the case head also fell out and I noticed the rest of the case still stuck in the chamber. When I got home to clear the chamber, the rest of the case fell out by itself when I opened the bolt.

I've been hand loading pistol cartridges for the last 25-30 years. Nothing fancy or fire breathing. Other than a few split cases or light primer strikes, I've managed not to blow myself up (as my granddaughter once informed me I might) - at least not yet. This is a first for me.

So, my question is - what can cause this? A quick web search pointed to excessive head space so I guess I need to learn how to check that.

I don't think the load was a problem. It's toward the upper end of all the info I could find, but looks pretty mild for 357 Magnum.

I usually only reload my brass 5 times max before replacing it. I had previously found a resized case that had an obvious crease right where the problem round separated and had set that aside. None of my other resized brass or reloaded rounds show that same crease. Below are measurements of different cases near the base and about halfway up the case, starting with a factory round for reference and compared my handloads.

Top to bottom
Federal factory 158 JSP .3750" .3750"
Unfired handload 158 SWC .3775" .3730"
Sized handload case .3775" .3730"
Fired handload case .3775" .3830"
Separated case .3770" .3820"
Creased sized case .3775” .3730"

I use Lee dies for my reloading. Is it possible that the resizing die is too small and is necking the case down too much - maybe weakening the case with excessive bending and creating a stress point? Kind of like flexing a thin piece of metal back and forth until it finally breaks?

Open to all suggestions,
Pete

[BigAl52]

On the bottom piece of brass I see what appears to be a ring around the brass. Am I seeing that correctly?

[azdover]

Yup. That’s the one I had noticed previously after sizing some brass. It’s measurements is the last entry in my list of measurements.

[BigAl52]

That doesn’t look good to me. Ive got Dillion Square Deal dies and RCBS single stage carbide sizing dies and I dont get anything like that on my brass. Does it do that on all the brass when you resize it or just every once in a while

[azdover]

First time I've ever seen that crease/ring on a resized case. I didn't notice anything like that on the case that separated but it may have been there and I just didn't catch it. I've checked some of my other cases, both fired and resized, and haven''t found any more. It looks like the crease/ring occurs where the sizing die stops resizing the case just short of the base of the shell.

After a little more research, it looks like head case separation can happen occasionally in 357s with excessive head space, particularly rifles but not revolvers. Looks like it's time to whip out the plastic and give Brownells some more business for a set of go/no-go gauges.

[5shot]

I've never seen a case separation like that in a straight wall pistol cartridge and don't know anything about Xtreme bullets. Your fired rounds are a couple thousands bigger than the cases I just measured but your handgun velocities don't seem to be out of line. Looking in the Hodgdon manual I see their maximum load of CFE Pistol under the 158 XTP is 6.9 gr for 33,700 PSI. Could it be that the combination of seating depth, primer and powder charge is too hot?
The Savage 99 was known for case separations with warm loads. I helped a guy at the range extract a case from his .250/3000 Savage a couple weeks ago. If the Henry action exhibits that same "springyness" with higher pressure loads could the case walls be clinging to the chamber while the case head is backing up a bit? Just thinking out loud here...
CFE is a relatively fast burning powder in the .357 case and I wonder if it doesn't go from mild to wild quickly. I've got some .357 brass with well over 20 loadings but after a half dozen or so of full throttle stuff it gets "retired" for use with mid-range loads.
For what it's worth....

[rickhem]

Unfortunately, my work firewall is blocking the pictures from being viewable here. I'll have to check this out when I get home later. But that said, glad you are safe and you did the right thing by stopping and figuring out what happened.

Having been experimenting with some stout loading trials on my own .357 BBS, I'm paying attention here. Most of my warmer loads have been with either Lil Gun, or 296, and honestly way more Lil Gun than anything. So far, I haven't had any issues with the brass, and the brass I've been using for these warmer loads is a mix of RP, PMC, and GFL (Fiocchi). I say mixed because I load the same load in different cases, but do keep them segregated by headstamp during the process. Sometimes one specific case seems to give better results.

I've had case head separations in my AR15, shooting .223, and the first time it caught me completely off guard. The other guys on the line treated it like no big deal, a few had a little removal too for the top of the case that was still stuck, and the general consensus was that "it happens". I even got an alibi out of it. So I doubt your rifle has any damage, if that is a concern.

A .357 headspaces on the rim, so the condition that would cause a case head separation in a bottleneck cartridge is completely different than what you had. I'm going to have to get back to this after I can see the pictures and think about it a little.

[CT_Shooter]

First time I've ever seen that crease/ring on a resized case. I didn't notice anything like that on the case that separated but it may have been there and I just didn't catch it. I've checked some of my other cases, both fired and resized, and haven''t found any more. It looks like the crease/ring occurs where the sizing die stops resizing the case just short of the base of the shell.

I've marked this image to suggest the reloading process may be the cause, as you suspect. It seems that the reloaded cases have each been affected somehow. Interesting problem. Please keep us posted. Thanks.

What's causing this mark on the Case?

Handload Cases.jpg (111.02 KiB) Viewed 2199 times

[DsGrouse]

Let me guess: you are using carbide resizing dies. I get a similar ring. I don't load my plated that hot, most of my shooting is subsonic. My load is 4.8 grains of cfe p. coal 1.455 for an average of 944.5 fps.

I'm thinking of going to a steel-sizing die because of this ring issue. I get this same issue with Lee, RCBS and redding carbide dies.

I sized a couple. There are four new unfired Starline cases and four fired Starline cases.



I am betting there is some work hardening happening with the brass at that spot. When fired, it seperates.

Looking at your load data, you don't have a high pressures according to GRT. That is, if, IF, your brass holds the same 27.30 grains of h20 that mine does.


It looks like peak pressure is 18,230 psi.

From what I gather, a lot of that is due to Henry. The initial bullet jump reduces pressure compared to a similar system like a revolver. I didn't bother adding in the bullet jump into this equation as your rifle might be different than mine.

with a 180 grain bullet, 1.575 coal, my bullet jump is 0.3500 to the lands. That brings my peak pressure down quite a bit.

[CT_Shooter]

Just checked a few of my hand loads and they have the same ring. I use Lee carbide dies and I never noticed it before. Thanks.