Semi Bren Primer Flow

[alterego]

Peter, please look at the corners of the primer, they don't look flattened...at least to me. Otherwise, yes it looks a bit ugly.

Please bear in mind that a semi is a bit different than the full auto gun as well. My firing protrusion looks correct (was same as standard pin too). However the firing pin (aft end) was about 2mm too long. So in a full auto gun the piston post whacks the firing pin, and gets it moving at whatever velocity that impulse gives it, then impacts the primer pin at whatever momentum the firing retains at primer impact. (I know you know this, just spelling it out in case _I_ have gotten something wrong)

In the semi gun, the bolt closes, the moving mass is the striker, telescoping section of the recoil spring and half the recoil spring's mass. Bear in mind that the striker is propelled by say 1/3 the total of the recoil spring force. So I think it's safe to say that it is at least a possibility that the semi striker is imparting a greater impulse to the firing pin than a full auto gun.

Now, all that being said, the aft end of my firing pin was ~2mm too long (sigh). So rather than hitting the primer with just the momentum of the firing pin's mass x its velocity, the pin is hitting it with whatever velocity remains x the mass of the striker, telescoping recoil section, half the spring AND the firing pin.

I've shortened the aft end of the pin for about 0.35mm free play, hopefully I don't get light strikes. I'll shoot it and take photos again.

As for other questions I might have missed, the ammo is new and known to be a good load (NATO M80 I think).
Headspace is where I set it at build about 0.003" loose from go (can be forced closed on no-go gauge), chamber is good condition (chromed).
The firing pin is a modified full auto pin (tail added to pin).