Breech face pitting

[Bluemooncricket]

I'm loading WST with 124 gr MG fmj and BBI with mixed range brass and Winchester spp to minor power factor and noticed some pitting on the left side of my m&p 9's breech face. In the brief research I've done, this problem seems to be related to the use of magnum/rifle primers or major power factor loads, neither of which is applicable in my case. Could loose primer pockets be my problem? I load on a 550 and don't really notice any one head stamp being more or less difficult to seat primers. Is there a visual cue to a loose primer pocket? And lastly, is it common to have the pitting on only one side, or could this just be a defective slide? Sorry for the long post and lack of pics. Thanks in advance!

[magpulled]

Loose primer pockets and I've had it happen with crimped primer pockets when I didn't get the crimp out good enough.

[Bluemooncricket]

Is there any visual clue I might detect in my fired casings that would indicate a loose pocket?

[Gandof]

Loading on a 550 you should be able to feel a primer seat. If they go in too easy, the primer pocket is likely a bit loose. I've seen pitting on the breech face from blown primers, but haven't seen any pitting caused by loose ones.

Gandof

[kamikaze1a]

My breech has a nearly complete circle the size of a small primer around the striker opening. If you use a load that does not have enough pressure to obturate the primer cup, you could see gas cutting of the breech face. In your case, parts of the breech face must be softer since the gas cutting is isolated. I doubt that it could be the casing or seating causing gas to erupt at only that one spot as the case positions at random with each cycle. Gas must be escaping 360° but cutting only in that one spot.

What does the outside of your fired casing look like? Is it sooty or clean?

[Red Ryder]

Send the gun back to the manufacturer! This can't be common. ??????????

[Bluemooncricket]

When I started working up the loads I had a few cases that were "sooty" at the mouth. The charge weight I've settled on burns much cleaner, especially with jacketed bullets.

[mgrs]

I'd also like to crack the code on this. I've never experienced it with anything other than military surplus corrosive ammunition but am always watching for it.

You'd think that a powder as fast as WST, even in minor, would generate a high enough peak pressure to seal the primer.

I've been doing some experimenting with this recently and can't figure out what might cause it. I loaded a couple hundred some sub-minor plated and cast with small rifle primers in varied pick-up brass, and had no gas marks on the breech face. There was not enough pressure to cause primer flow even in a glock. I have loaded thousands of .45 acp at low major pressures with mag pistol primers and also have never seen breech face marks.

[superdude]

Is this maybe a headspace issue? I admit I'm stumped by this and now having someone have this same problem with standard pistol primers just adds to the mystery. In some thread here, or elsewhere, someone suggested that headspace might be behind this. Under this hypothesis, excessive headspace allows the primer to back out of the case far enough to allow gas to escape around the primer before the case is pushed back by the pressure to re-seat the primer. I thought it was an interesting if not downright elegant explanation.

Bluemooncricket, could you maybe take a look to see if you have too much headspace? Don't ask me how to do this, except maybe drop loaded rounds in the chamber and see how far the base is from the breech face / end of the barrel hood.

[Sandbagger123]

if you could take a picture of what you are concerned about that would help a lot. That being said, all my heavily used 9mm have some pitting on the breech face. its the finish worn off and gases after thousands of rounds.

[Bluemooncricket]

Sure thing! That's a theory I had never considered. I suppose the best way to measure would be with a feeler gauge between the barrel hood and breech face and then from the cases base to the end of the barrel hood.

I've inspected my spent cases but I haven't really noticed anything peculiar on the primer end.

[Bluemooncricket]

I'd be happy to post a pic if someone could tell me how.

[kamikaze1a]

When I started working up the loads I had a few cases that were "sooty" at the mouth. The charge weight I've settled on burns much cleaner, especially with jacketed bullets.

If your cases are showing a lot of burnt black on the outside, the loads pressure may not be sufficient to expand the case and seal the case to the chamber. Increasing the crimp should delay the bullet long enough to cause the case (and primer) to expand and better seal... If your cases are only black near the mouth probably not the case.

My experience with excessive headspace and primers backing out has been that the primers appear to be flattened like excessive pressure and sometimes even be pierced. The firing pin drives the round forward, ignition upon bottoming forward, the primer backs out before the case is driven back by the ignition pressure and flattened against breech. You can display this by loading and firing a case with primer only, no bullet or powder. The primer will usually back out a bit...

[superdude]

I'd be happy to post a pic if someone could tell me how.

Try a simple copy and paste. That actually worked for me recently. Otherwise the other way is to open an account (free) at some place like photobucket. You can upload figures there and then copy the url to this window.

[Sandbagger123]

Here are some pix of my MP9 and G34.

[Bluemooncricket]

Sorry for the cell phone pic but my camera is broken. I measured the clearance between the barrel hood and breech face to be .007. Five different rounds I tested were all flush with the barrel hood. Just to be clear, this gun has never been stellar at 20 yard groups, 4" or 5", but is pretty much on par with most of what I've seen from 5" M&P 9's.

[superdude]

I'll have to let the gunsmiths or more experienced people chime in on this since I've never measured headspace but .007" sounds like a small number to me.

[Bluemooncricket]

I'll have to let the gunsmiths or more experienced people chime in on this since I've never measured headspace but .007" sounds like a small number to me.

I was also unsure of what would be within spec for an M&P. The barrel fit is a bit loose compared to my 1911, but I would expect it to be.

[kamikaze1a]

During this current component crunch, I wanted to save my sp for matches and burned through 10k of sr primers for practice rounds. My pistol load's pressure couldn't seal with the harder rifle primer cups and left gas cutting on the breech face. The cut is nearly a full circle the size of the primer encircling the striker hole.

Firing a case with just the primer and then measuring how far the primer backed out would give you a good representation of your headspace. If your case's flash hole is too large, the primer may not back out.

[lugnut]

I had this happen to a Sig when I first started reloading. Never did figure it out.... But I was using CCI primers. I use Feds now almost entirely. Some get pretty flat too. Never a problem.

I think it's definitely from lack of primer sealing from hard primers. What powders exacerbate this behavior is beyond me.

I use fast powders, heavy bullets and Feds without issues.

Edited August 30, 2013 by lugnut

[rhyrlik]

Is this maybe a headspace issue? I admit I'm stumped by this and now having someone have this same problem with standard pistol primers just adds to the mystery. In some thread here, or elsewhere, someone suggested that headspace might be behind this. Under this hypothesis, excessive headspace allows the primer to back out of the case far enough to allow gas to escape around the primer before the case is pushed back by the pressure to re-seat the primer. I thought it was an interesting if not downright elegant explanation.

Bluemooncricket, could you maybe take a look to see if you have too much headspace? Don't ask me how to do this, except maybe drop loaded rounds in the chamber and see how far the base is from the breech face / end of the barrel hood.

For what you say to happen, the headspace would have to be .100"