40 S&W Case Head Separation

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docbrown

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Was visiting my family in SC last week and took an afternoon to go to the range with my brother. Last round in the magazine of my M&P Compact gave me a slight case of "Black Face". Once I got the unejected piece of brass out, I examined the gun and there was no damage. The load is as follows:

8.9 grains of Longshot
Winchester SPP
155 grain Ranier Plated Flat Point
COAL 1.125
Temp on the day this happened 93 degrees
Temp on day of load development 85 degrees/87 degrees

All rounds loaded on a Lee 4 hole Value press with a Lee Taper Crimp die finishing the process with just enough crimp to remove the bell. All rounds run through a Lyman cartridge checker and passed the plunk test. I also weigh each case before I charge it with powder, tare the scale before removing the case, charge the case, and then weigh to check the charge weight.

Worked this load up using Hornady data, starting at 7.5 grains working up to 9.5 grains in .5 grain increments. (max according to Hornady was 9.6 grains). Stopped after 3 rounds when I got to 9.5 because I was getting flowing primers. No pressure signs at 9.0 grains. Dropped to 8.9 grains and tried it and was very accurate and gave me 1130 FPS out of the 3.1 inch barrel.

Not necessarily chasing velocity, more interested in accuracy. This load seemed the most accurate without pressure signs and then this happened. Other cases do not show pressure signs and the mark on the primer in the picture looks like primer flow, but I get that mark even with starting loads - just a "finger print" for this particular pistol.

I am thinking a bad piece of brass (range pickup, so no real history on it), but being a belt and suspenders kind of guy, I am thinking of pulling down what I have loaded, checking the powder charge with a different scale and perhaps dropping down another couple of tenths of a grain of powder.

Thoughts? I have seen similar pictures in my research and the opinions range from bad brass, to too hot of a load to firing out of battery. Would like to hear what my Highroad peeps have to say.

20220613_213504.jpg 20220613_213518.jpg
 
Well you are not using a "Hornady" bullet. So that data is not relevant
Your bullet is not the same as a XTP

Could just be a bad piece of brass who know what kind of life it had,

Error, start over,
 
Bad piece of brass, check the ground around your range there should be a bunch more good cases laying around. Watch the next few rounds to see if the issue repeats.
 
Just cut your loads. Physical pressure indications are very unreliable, and it is my opinion, that when you see them, you are over max pressures. I have seen a lot of case head blow outs, such as your picture, and when a case head blows out around the extractor groove, that is an indication of excessive pressures, massively excessive pressures.

I do recommend shooting some factory ammunition over a chrono, and then keeping your velocities below that. Factories use powder lots and blends we don't have access, so they can optimize velocity, without going over pressure limits. We can't. We reloaders have powders that are not infinitely varible in burn rate, and since we don't have pressure gauges we really don't know what is going on. Sort of like trying to measure to 0.001" with a yard stick.

The 40 S&W is a hot cartridge from the factory, from everything I have read, it is right on the red line, so to say. Won't take much to push it over the line. So, cut your powder charge by a half a grain, to a grain.
 
Years ago - about six - I had a similar case failure. .40 S&W caliber round.
Load was 180 grain cast lead bullet, 5.4 grains WW231 and a CCI standard pistol primer. (Load data from Lyman #50; maximum load is 5.8 grains of WW231.)
Pistol was an H&K USPc, unaltered.
I was shooting in a bowling pin match and had successfully cleared several stages. I'm not the fastest, but I hit pretty well. My last shot for the day knocked over the last pin. The recoil felt odd. About the same recoil surge, but 'odd'. Clearing the pistol, the slide was not fully closed. The case head separated from the body, leaving the body (the forward 'tube' part) in the chamber. The extractor was broken. (I did find all the bits and keep them in a used but clean prescription bottle.)

All the other rounds functioned normally. They fed through the magazine, chambered, fired and ejected in the expected, normal manner. The report was not noticeably distinct from any other shot. The Range Officer was standing about six to eight feet away (running the match) and did not notice any audial deviation from typical. As mentioned, the recoil was normal - not excessive - other than the slide not closing fully.
I did collect the other fired cases. Nothing unusual to report. No indications of high pressure or cracking.
My considered opinion is the case was 'faulty', but had been fired once or twice prior without incident.
I know someone will ask what brand of case. Winchester or Federal is all I have.
 
Questions I would ask myself.
1. Is my powder charge weighed or thrown... how consistent.
2. Is my gun having any function issues.
When this happens in an auto pistol my first inclination is a barrel that is not fully supported, and second is that the round was not at full battery.
 
Bad piece of brass!

Not common, but does happen.
Watch out for “Glocked” brass. Throw out any brass that doesn’t look right.
 
AJC1 said:
Questions I would ask myself.
1. Is my powder charge weighed or thrown... how consistent.
2. Is my gun having any function issues.
When this happens in an auto pistol my first inclination is a barrel that is not fully supported, and second is that the round was not at full battery.
Click to expand...

1. Both thrown and weighed - as mentioned in the OP I throw it on the press but first weigh the case, tare the scale, throw the charge and then weigh to verify the charge. If it is not exact, I throw the charge again until it is. I use a Hornady electronic scale, so it is possible it is off plus or minus .1 grains.
2. No function issues. Went through 50+ rounds of the same load that day without even a hiccup.
3. M&P 40C does have a fully supported barrel
4. I do not think the sear can clear if the slide is not fully engaged (I could be wrong)
 
docbrown said:
1. Both thrown and weighed - as mentioned in the OP I throw it on the press but first weigh the case, tare the scale, throw the charge and then weigh to verify the charge. If it is not exact, I throw the charge again until it is. I use a Hornady electronic scale, so it is possible it is off plus or minus .1 grains.
2. No function issues. Went through 50+ rounds of the same load that day without even a hiccup.
3. M&P 40C does have a fully supported barrel
4. I do not think the sear can clear if the slide is not fully engaged (I could be wrong)
Click to expand...
The point is systematically eliminate variables until only the answer remains...
 
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