Cratering on primers

[Bora72]

Hi everyone, I was doing some reloading tests for my 6.5x47 Lapua with RS50 and 139gn Lapua Scenar, Fiocchi SRM primers.
The range of the loads are from 35gn to 37gn. OAL 71.2mm(2.803") (freebore zero 71.5mm(2.815").

For the foulers, I used 120gn PPU bullets and a 36.5gn load, OAL 66.7mm(2.626"), same Fiocchi SRM .

Looking at the primers, I noticed that even the lower loads using Scenar had some cratering.

The primers for the foulers, however, did not. I think it could be due to the difference in initial pressure.
Scenar ammunition, which is almost in contact with the throat, are longand for this have major initial pressure than the foulers, which are physically shorter and therefore further from the throat and have less initial pressure.

What do you think could be the cause?

Thank you

 

[randyc]

I have used Fiocchi srm for practice and fireforming PPC rounds, seems like they are softer than the federal 205 that I used wirh match loads. The foulers you use probably had less presure than the 139 gr loads.

 

[William Vogel]

Your fouler loads should be the same powder and bullet as your regular ammunition. The reason is that the graphite in the powder and the copper from the bullets needs to be identical because it’s deposits in the barrel are what foul the bore and using different stuff defeats the purpose of the fouler.

Primer cratering is a product of the firing pin hole in the bolt face generally being to large and having a loose fit to the pin diameter and possibly having a chamfer. Bushing the bolt face and reducing the firing pin to 0.062 fixes this.

 

[Bora72]

I have used Fiocchi srm for practice and fireforming PPC rounds, seems like they are softer than the federal 205 that I used wirh match loads. The foulers you use probably had less presure than the 139 gr loads.

Hello, thanks for the reply!

Ok for the opinion about the Fiocchi SRM.

Less inertia/initial pressure = bullet away from the throat?

 

[Bora72]

Your fouler loads should be the same powder and bullet as your regular ammunition. The reason is that the graphite in the powder and the copper from the bullets needs to be identical because it’s deposits in the barrel are what foul the bore and using different stuff defeats the purpose of the fouler.

Primer cratering is a product of the firing pin hole in the bolt face generally being to large and having a loose fit to the pin diameter and possibly having a chamfer. Bushing the bolt face and reducing the firing pin to 0.062 fixes this.

Thanks for your advice

 

[Coyotefurharvester]

Too much headspace
Bolt face/striker fitment
Soft primers for rated pressure max of the cartridge.

 

[Bora72]

Headspace are 2mil less than the fired brass.
Space from striker and hole of the striker can are a clue.
The load can I've used on the 139 Scenar have less pressure than the load of the 120gn bullet load.

 

[Jason D Hostetter]

What action?