cast flash hole

[milsurpshooter]

Still playing with my new 300 BO upper,working of forming cases from 223 rem ,very laborious task,anyway according to C. E. Harris the brass used exclusively for cast should have the flash hole enlarged to 0.099 to prevent shoulder set back.Same reasoning for the 300 BO am i safe to assume?

[fatelk]

I think that would depend on pressure. My understanding is to enlarge flash holes for low pressure cast loads to increase the pressure in the primer to avoid primer back-out and shoulder set-back (I could be wrong though since I never have done this.)

In full pressure loads, cast or jacketed, there wouldn't be any need to enlarge the flash hole. I've never played with the .300 BO, but I assume the cast loads would be standard pressure in order to cycle the action?

[runfiverun]

gas volume is what does the work not pressure.
the 300 does best with the short carbine/pistol length gas tubes.

[Scharfschuetze]

CE Harris was correct when loading squib loads in bottle neck cartridges, but only for very light or squib loads. The advice does not apply to high pressure loads.

The pressure in the primer pocket from the detonation of the primer is greater than the pressure of the expanding gas in the cartridge case and it pushes the case forward into the chamber and thus collapses the shoulders of bottle neck cases with the squib loads. The collapse can be gradual and only occur after a few to several loadings, but it is very noticeable if you keep track of such things. RCBS, Hornady and MO's gauges are useful in measuring the shrinkage of the headspace. Mo's gauges are my favorite and do double duty in checking the headspace of my individual rifles.

Once your HS starts shrinking in low pressure loads, you'll often see your primers starting to back out, which is often a clue as to what's going on.

I drill out my flash holes for very light loads in most of the bottleneck rounds that I load for. Keep 'em segregated from the cases for your higher pressure loads. While I've not found a great deal of difference between differently sized flash holes when testing over a chronograph with moderate to upper end cast boolit loads, there is some, so be safe and keep 'em separated.

Bottom line? If your are loading to normal pressure levels, don't bother to drill out your flash holes. If you are loading on the low end of the chart for your powder and boolit combination, buy one of the above listed gauges to track the issue, drill if needed and you'll be good to go.