Case rupture - What did I do wrong???

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Ocraknife

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Bullets: Hornady 180 JFP 10mm
Powder: Accurate #7 11 grains (max for this combo is 12 grains)
Primer: CCI Large Pistol Primer #300
Brass: Unfired Starline
C.O.L. 1.260"
Pistol: S&W 1076 4.25" barrel (first time I've shot this gun)

Can anyone tell me what I did wrong? I double checked several rounds and they weren't over charged and my bullet seating is correct as specified.

I didn't go over the max and the brass was brand new.

I thought maybe the rounds weren't head spacing right so I included a picture of them fitting in the chamber. They look about right to me.

There is no visible flaws in the chamber and the diameter of the fired brass (the ones that didn't burst) is a couple thousandths of an inch narrower than the brass that was fired in my Glock 20 (which I no longer have) so I assume the chamber is a littler tighter.

Take a look at where both cases failed, they failed in the same place.

I shot about 25 rounds and the last two were the ones that failed. The second to the last ejected and I had no idea that it had split. The last one ejected only the last half of the case and left the first half in the chamber. I couldn't fully chamber any more rounds which is how I knew it had failed.

Any suggestions? Did I do something wrong? Could it be a bad batch of brass?
 
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Did you measure the case length ? Even new cases should be checked & cut to the same length. Also checked in case headspace gage.
 
That is weird. I can't recall seeing straight wall cases torn in half, most unusual.

In my opinion, your load is too hot. If the breech pressure at unlock is high, and the case front is sticking to the chamber during extraction, that could be the problem.

Two ways to approach this, firstly cut your loads. Secondly, shoot some rounds with the cases dry and some lubricated. Take an oil bottle and put a drop of oil on every second or third round in the magazine. This will break the friction between case and chamber at normal pressures. I do this all the time shooting Bullseye Pistol with the loads in my 1911. Allows my pistol to cycle more reliably with light loads.
 
Very Similar Loading

With Hornady's 180 XTP, using *-* brass (new, in some instances), and CCI 300 primers, I have run up to the full 12.0 grains of AA#7 with no trouble.

Both Hornady 9th and Speer #14 maxes out at 12.0 grains. I settled on 11.7 grains as my set recipe only to have some safety margin - the 12's shot fine without any pressure signs. And I have since loaded and shot several hundred of the 11.7's through my G20sf & G29sf with no trouble at all. It's a fine shooting round.

I load them to an OAL of 1.255". But that's kind of apples n oranges as we're using slight different bullets and guns.

I'm not going to guess at the problem. A bad batch of brass is a possibility, but I'm not saying it is. I'm only chiming in to let you know there's a guy out there who's loading a very very similar round with no trouble at all.
 
New brass from Starline should be good to go. They have been very consistent for me.

I think you should consider the 11.0 gr charge of AA#7 to be in no man's land.

Might want to call the max charge for your gun to be 10.5 gr AA #7.

From the attached photo, your rounds passed the plunk test just fine.

Remember, what works in a test gun at the ballistics lab won't necessarily be OK for your gun, and vice versa.
 
Did you measure the case length ? Even new cases should be checked & cut to the same length. Also checked in case headspace gage.
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I didn't. measuring a few now I see that some are off by one thousandth of an inch. I'm embarrassed to say this but I didn't even know I needed a headspace gauge.
 
New brass from Starline should be good to go. They have been very consistent for me.

I think you should consider the 11.0 gr charge of AA#7 to be in no man's land.

Might want to call the max charge for your gun to be 10.5 gr AA #7.

From the attached photo, your rounds passed the plunk test just fine.

Remember, what works in a test gun at the ballistics lab won't necessarily be OK for your gun, and vice versa.
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I agree. I'm not going to go that high going forward and this will not stop me from using starline going forward.
 
When you look at the unfired primer vs the fired primer, is it just me or does the fired primer look like it is flattened, as if it were subjected to overpressure?
 
This -
the case front is sticking to the chamber during extraction, that could be the problem.
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Clean the chamber. See the dimples in fired brass? Brass is sticking. Reduce the powder charge so brass can spring back after firing for easy extraction. Start at 9.6 gr. The tight chamber will increase pressure. I blew 44 mag brass in half before.
 
The fired primer looks like it may have primer wipe. The firing pin is in contact with the primer as the action is opening. Normal on some guns. Other wise, it looks ok Primer wipe" is a teardrop-shaped firing pin impression, accompanied by a drag mark (scratch or gouge) following the "point" of the teardrop and leading away from the primer, sometimes into the brass. This is because the firing pin does not fully retract after the round has fired and the slide is traveling back during ejection, causing the case to drag across the firing pin as it is thrown clear. It is not in any way harmful, except sometimes to the case if the primer pocket edge is gouged. Kahr will tell you it is a normal condition for their pistols, even saying so in the owner's manual.
 
Clean the chamber. See the dimples in fired brass? Brass is sticking. Reduce the powder charge so brass can spring back after firing for easy extraction. Start at 9.6 gr. The tight chamber will increase pressure. I blew 44 mag brass in half before.
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I'm sorry. I'm new to this. Please help me understand what I need to do. I know the chamber was clean before I shot so if I understand properly, I need to drop my charge down substantially correct?
 
the last two were the ones that failed.
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A dirty chamber , with high pressure , in my guess. I would load 3 rounds at 9.6 gr , go out back , fire them to see if they work the action. Start from there.
 
A dirty chamber , with high pressure , in my guess. I would load 3 rounds at 9.6 gr , go out back , fire them to see if they work the action. Start from there.
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Understood. I can do that. It may be toward the end of the week before I can make that happen but I will report back on my results.
 
I'm not convinced that it's pressure related. Rough chambers are found on a whole lot of pistols. The amount of pull that was needed to neatly rip that off in that ring would have been incredible, it should show as a gouge in the rim, I think.

It's not at the base of the bullet. Why would it have torn off so perfectly in the exact place, twice? The way there are fine shreds of brass on the tips of all cuts surprised me.

I am having a really hard time putting this to load error, because I'm just not seeing problems serious enough to cause it, and brand new brass should have been too strong to pull apart like that unless there was already a weakness.

I can't explain it, but I don't think that pressure and a dirty chamber combined would have done it. I can't imagine what sort of flaw in the brass could have caused it.

You should, IMO, inspect all of the remaining cases as carefully as you did these. Take a really good look at your chamber, as well. Have you used the gun very much?

Imo, you MUST contact starline and have them look T this. If there is a problem with the cases, they need to know.
 
It's important to note that when a bottleneck case is stuck, has anyone pulled off the case head? I'm sure that it could happen with old brass, but this just doesn't look right.

I've even got a paranoid feeling that he made this story up to keep us up all night.
 
I concur about measuring case length after resizing, see where you are relative to specs.

Is it possible to get a closer pic of your crimps? What type crimp are you using?

Normally the plunk test in the barrel is good enough, but in your situation a case gage may be a good idea.

Agree with backing off max load for testing a new set of reloads.
 
When you look at the unfired primer vs the fired primer, is it just me or does the fired primer look like it is flattened, as if it were subjected to overpressure?
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The fired primer in the photo looks A-OK. I do not see signs of any high pressure from that.

I need to drop my charge down substantially correct?
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Be careful here and do not drop charges below the recommended start loads.
Myself would drop maybe 0.5-1.0 gr. and give it a try.

I'm embarrassed to say this but I didn't even know I needed a headspace gauge.
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You don't. IMO, a waste of money. If you buy anything in this regard, buy a good quality caliper. With practice, you can keep up with anyone using a headspace gauge.

It's important to note that when a bottleneck case is stuck, has anyone pulled off the case head? I'm sure that it could happen with old brass, but this just doesn't look right.
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I have even pulled a bottle neck case apart in a sizing die as well as a chamber. Only problem is, were are into straight cases here, so not much correlation.

Rough chambers are found on a whole lot of pistols.
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The only rough chamber I have ever encountered was in a rifle. The only one.

You only had two cases that created a problem. I don't think that would indicate the whole batch of brass is defective.

Measure the cases, maybe every 5th or 10th one and get a feel for the brass. One thousandth is not going to create any problem.

I have loaded over 100,000 handgun cartridges spanning a 54 year career in the hobby and I can honestly say that I have never trimmed even one and I have never owned a case gauge of any sort. I haven't destroyed any guns either.

Just reduce your charge by an amount that makes you feel comfortable and give it a try. Just remember, don't reduce too much.

The only thing really to worry about is if the cases have more separations, take care of it as the gasses will eventually cut the chamber.
 
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