Sig P220 - Double Firing Pin Strike

[Werewolf]

I reload .45ACP.

My two loads are:

1) 5.3gr HP38 under 230gr FMJ Fed 150 primer
2) 8.5gr AA#5 under 230gr FMJ Fed 150 primer

Both loads are well under SAAMI spec for the .45ACP according to published data.

I shoot load 1 out of my Sig and load 2 out of my S&W 1911.

When shooting load 1 out of the Sig I often find a small secondary dimple in the primer that intersects the firing pin dimple. In other words it kinda seems like the pin is hitting the primer twice. When shooting load 1 out of the 1911 no such double hit is happening.

Question: I shoot Hornady .45ACP +P 230gr XTP's out of the Sig and don't get the apparent double strike. Is this a double strike in the Sig resulting from high pressure or is something else going on?

I'm betting on something else since the load works fine in the 1911 and a +P load works fine in the Sig.

What could be happening here?

 

[Jim K]

Hi, Werewolf,

A picture would help. I can think of several reasons, but prefer to wait until I can see a picture. Have you modified the gun in any way, like changing the hammer spring (mainspring) or the firing pin?

Jim

 

[Werewolf]

Can't provide a picture.
Don't have a digital camera.

Imagine the firing pin dimple in the primer. Then imagine a smaller semi or quarter circle dimple at the edge of the main dimple and you've got what's happening.

As an aside I posted the same message in the Handloading forum because the effect I mention is often a sign of over pressure. Two replies received both saying the problem is very common to Sigs.

 

[Frohickey]

Are you sure that its a small secondary firing pin strike?

Or does it look as if its like a teardrop primer strike?

Sigs, I have read, are supposed to keep their firing pin out a little longer to prevent debris from getting into the breechface.