9mm M&P EZ Breech Face and Primer Strike Issue

[msgdan]

New 9mm EZ out of the box, just bought on Saturday. The breech face has a groove directly under the firing pin hole. This leaves a corresponding mark on the bullet primer. Has anyone seen this before? No other marks on the brass. No issues with feeding, firing, extracting or ejecting. Thoughts?

[Fastbolt]

Are you talking about the "teardrop" shaped machining of the bottom, and directly below, the firing pin hole?

If so, that was a refinement introduced in the M&P series pistols some years ago. It helps prevent metal shavings being cut from the case rim as the round slides up the breech face during feeding, and shavings cut from the primer cup as the case slides down during unlocking after being fired. This helps prevent excessive metal shavings from entering and accumulating inside the striker channel.

In older days savvy smiths or armorers might've use a long-shanked drill bit (of a specific size) to reach in from the muzzle end of the slide to gently "break" the sharp edges of firing pin holes in breech faces to accomplish the same purpose.

[msgdan]

Fastbolt,

That is exactly what I was talking about, the teardrop shaped machining. Thank you for your information. That puts my mind at ease.

Dan

[Fastbolt]

Originally Posted by msgdan

Fastbolt,

That is exactly what I was talking about, the teardrop shaped machining. Thank you for your information. That puts my mind at ease.

Dan

De nada.

As I recall, they started slipping it into the machining of some of the M&P's back about 2010-ish, and then we started seeing it across the caliber/model lines later on.

[Steve912]

Originally Posted by Fastbolt

If so, that was a refinement introduced in the M&P series pistols some years ago. It helps prevent metal shavings being cut from the case rim as the round slides up the breech face during feeding, and shavings cut from the primer cup as the case slides down during unlocking after being fired. This helps prevent excessive metal shavings from entering and accumulating inside the striker channel.

Is the relief normally that generous?

I ended up doing something similar on my Sigma .40.
It had a square-cut striker aperture, and shaved primers
& case heads (mostly on extraction/ejection) zealously,
filling the striker & safety plunger bores with only a
couple of hundred rounds. I put a barely visible bevel
on the lower edge of the opening, and it did the trick.

[Fastbolt]

Originally Posted by Steve912

Is the relief normally that generous?

I ended up doing something similar on my Sigma .40.
It had a square-cut striker aperture, and shaved primers
& case heads (mostly on extraction/ejection) zealously,
filling the striker & safety plunger bores with only a
couple of hundred rounds. I put a barely visible bevel
on the lower edge of the opening, and it did the trick.

Even Glock finally realized they needed to do something in that regard, and started beveling the 4 edges of the breech face hole in their pre-Gen5 slides. (Newer Gen5 FP's have rounded tips, at the request of the FBI, reportedly to help mitigate the potential for a chisel tipped FP to perforate primers, as that can become a problem with "green" ammunition and gas erosion of the breech face and FP tip.)

I just went and pulled the slide off my 40C, which is 10+ years old, as I recall.I took some quick pics to show you the breech face from different angles & light.

[msgdan]

Thanks again for all your help.

[oldiegoldie]

nice photography.

[Fastbolt]

Originally Posted by oldiegoldie

nice photography.

My son got tired of me using my Nokia Windows phone and bought me an Apple. Better camera and software.

[Steve912]

Originally Posted by Fastbolt

My son got tired of me using my Nokia Windows phone and bought me an Apple. Better camera and software.

Great pics!

Guess I could revisit that Sigma and do a bit more.

Really should SHOOT it, a bit more...first!