Signs of Over-Preasure in .40 S&W?


April 19, 2009, 08:26 PM
I just finishred cleaning and sorting some .40 S&W brass that I fired at the range today. As I was sorting it, I noticed that there was an unusual raised area around the strike dimple. Under a magnifying glass, it became clear that this area was formed by the primer pressing on the firing pin hole. The outline of the firing pin hole from my M&P was clearly imprinted on the spent primer. I immediately began to wonder if these loads were too hot. I used CCI 400 small rifle primers (in the absence of SP primers) and 5g of 231 under a 180g. Winchester TC. Has anyone observed this type of thing before and is it an indication of over-pressure?


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Jim Watson
April 19, 2009, 08:36 PM
I do not load .40 and cannot give detailed information, but just so a .40 user will know what you are talking about...

.5 grain is not a feasible powder charge.
5 grains is Winchester's maximum load in the pre-Hodgdon booklet I have. A rifle primer would not increase chamber pressure a lot, but it will some. Do you have a reason for going to the maximum?
.5 gram is 7.7 grains, a gross overload.

April 19, 2009, 08:51 PM
Hi Historian,
I load for 40, quite a bit. Keep in mind that this is a pretty high pressure round at 35,000 psi... it matches 357 magnum and 41 magnum in pressure. If it was 5g of W231, that's a warm load.. with just pistol primers. If you must substitute a rifle primer for a pistol primer, I'd begin at start loads, which is why the name "start" is there.

As the reloading sages here will tell you, if you see overpressure signs in a pistol, you're way the heck over pressure. Running over pressure in a pistol won't necessarily give any signs, which is a great reason to not push your luck. Not to sound harsh, but if economy is a factor in reloading, you save quite a bit by not blowing your gun up. Be safe!

April 19, 2009, 09:06 PM
Thanks Jim, meant to say 5g which is the starting weight in Lyman # 48. Agreed Floppy, blowing up the gun is not cost effective which is why I posted in the first place. No offence taken.


April 19, 2009, 09:30 PM
Just about every factory load .40 I've shot will do exactly as you describe, primer flow into the firing pin hole ... I think it's just a function of a high pressure round. Although most I've seen don't need a mag glass to notice, it's often quite obvious but still not a problem.

Stick with your load data, and if you want to push max levels then hopefully confirm with a chrono. Your load looks fine to me.

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