Home Forums Hunting & Shooting Ask The Gunwriters New brass/long chamber - what to do?

I have a push feed 9.3x62 with a maximum chamber, so I size fired cases using a +.010 Redding shell holder for best results. But when shooting with new factory brass (RWS), I get very flattened primers like is usually associated with excessive pressure, even with light starting loads. So obviously, the firing pin is driving the cartridge forward away from the bolt face before it fires, on firing the primer starts to back out, and then the case expands back, re-seating the primer but flattening it in the process.

Is this damaging the brass?

Should I "fireform" the cases with reduced loads and bullets seated long to keep the case against the bolt face?

Or is this a non-issue and I'm over thinking this?

One work around is to expand the necks to .375" and then size the brass just enough for a snug fit in the chamber. False shoulder set up.

This is the best method!!!!

You might have to size the neck up to more than .375, depending on the firing pin fall. A really heavy firing pin can still drive the case further into the chamber if the false shoulder is relatively small. Have had that happen on more than one rifle.

I use a false shoulder for any rifle that I buy which has more than minimal headspace on new brass. I find that .02" over is minimum (such as .358 to .375 and back), and .03 (such as .308 to .338" and back) is better. On firing, brass worked that way will expand where it is thinner, and you won't develop a stretch mark at the pressure ring (just beyond the heaviest part near the extractor groove).

9.3 mm is .366". Anyone have a suggestion on what I can use as an expander plug between .386" and .396"?

Looks like CH4D makes a .35" to .40" expander that should do the job.