Odd primer strike. Primer reading gurus take a look

[muncie21]

These are relatively low velocity rounds (168-172 PF) so I'm not worried about over pressure.  Just trying to understand the mechanics that are creating these marks on the spent primers.  Almost as if there's a force pushing from inside the case, removing the typical primer dimple.  Notice how the three primers in the center are flat, with almost no 'dimple'?  What would cause this?

 

Ignore the different primers in the pic, I'm seeing this on both the S&B (brass) and CCI (silver) primers.

 

[M1A4ME]

Hard to be 100% sure, but it looks like the pressure is forcing primer cup metal back into the firing pin hole in the breech face.

 

With a rifle that can be a sign of higher pressures or an enlarged firing pin hole in the bolt.

 

With a relatively low pressure pistol round????  Maybe the primer material on the "offending" primers is just thinner/softer than other primers.  Or the pressure is actually higher than you think.

[muncie21]

This 'anomaly' is specific to one particular pistol, which leads me to believe it's a difference with this gun.  The other guns (similar barrel length) spit out the normal, boring, standard dimple.

[GrumpyOne]

The firing pin hole in the breech face on the one gun is larger, and the gun that is causing this may have an under sized barrel/short throat causing some over pressure.

 

On another note, using power factor to determine a round is not over pressure is misleading. You can have severe over pressure (kaboom, even) using a fast powder and heavy bullet, without ever getting close to major power factor. Just because a primer isn't flattened does not mean that it is not over pressure. Google over pressure primers.

[muncie21]

Thanks for the feedback Grumpy.  I'll take a closer look at the FP hole.

[GrumpyOne]

11 minutes ago, muncie21 said:

Thanks for the feedback Grumpy.  I'll take a closer look at the FP hole.

If you want to see something odd for a primer strike, find someone shooting a Beretta 92 or similar. Even normal factory loads look like over pressure in those because of the firing pin hole in the breech face. These were fired from a 92.

[fbzero]

Looks to me like some light pressure signs.  This can happen in some firearms and not others with the same ammo due to tighter or looser chambers.  I have a Springfield 9mm 1911 that always shows pressure signs before any of my other 9mm pistols.   Lighter primer cups usually show this worse/sooner as you work your charges up.  CCI's generally have harder cups though, so if I started seeing that with those, I'd definitely back it off some.

[ChuckS]

12 hours ago, GrumpyOne said:

If you want to see something odd for a primer strike, find someone shooting a Beretta 92 or similar. Even normal factory loads look like over pressure in those because of the firing pin hole in the breech face. These were fired from a 92.

Weird. Is the hole beveled?

[slayer61]

OP,

   I have see seen your primers before also. Happens in only one gun

 

 

Edited November 26, 2018 by slayer61

[Intel6]

20 hours ago, GrumpyOne said:

If you want to see something odd for a primer strike, find someone shooting a Beretta 92 or similar. Even normal factory loads look like over pressure in those because of the firing pin hole in the breech face. These were fired from a 92.

 

That is actually pretty standard for a Beretta. The .40 version of the Beretta looks like that also. I think it is just the way they make the slides?  When the Border Patrol was still using the Berettas I would find all kinds of .40 bras that looked exactly like this. Funny,  the second Gen S&W autos also had a distinctive fired primer look back when they were in use. 

[rishii]

Check the Firing pin, the last time I saw that I had a Ti  firing pin in the gun, swapped it out with a extra long one and the problem went away, or did a good job of hiding it