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Primer Flash Holes

20 Apr 2019
@ 01:58 am (GMT)

Paul Leverman

Does anyone else do this? We all know how to condition our primer pockets. But what about the actual flash hole? For whatever reason, however long ago, I started drilling out the flash hole. I use a # 45 (.082") drill bit. I believe I use this size as it was the diameter that cleaned up all the brass brands that I use (R-P, FC, Win., Herters, RWS, Starline, Bertram), making it easier to have just one size bit.

I googled this and found an article on Chuck Hawk's page, written by Allen Schuh. Not sure what his claim to fame is, but it was an interesting article. Here is a quote:
"I am pretty careful about procedures. What I found was that the median impact at one hundred yards was one inch higher with the larger flash hole. I held everything constant except the size of the flash hole. This could signify a change in either velocity or the recoil impulse. It is also likely the result of a change in the pressure curve, which could be dangerous and almost certainly means the published reloading data is no longer valid. The bottom line: clean and (if necessary) deburr flash holes, but do not enlarge them!"

If you read the whole article, Mr. Schuh resized his flash holes from 5/64" to 8/64" (that is a huge jump, not to mention the hole size). Why he would go that far is beyond me, but it was his experiment. It was also obvious (to me, anyways) that his experimental process was flawed, but that is for another discussion if anyone wants to discuss it.

After resizing my flash holes, like any other change in procedure or components, I start my load developments over. Have always had safe loads, but never did a "before/after" . So, just curious if anyone has ever gone from "before" all the way through to "after"?


25 Apr 2019
@ 07:41 am (GMT)

Nathan Foster

Re: Primer Flash Holes
Hi Paul, yes, sounds like a dramatic hole size but it is always interesting to hear the results of oddball experiments. I guess its not too different to me firing some bullets backwards.

I use a K&M tool to uniform the pocket and the flash hole. I don't do this with all of my rifles / ammo, just my pets. Quite often, I just want to see how a rifle goes with only basic attention. This keeps my feet on the ground as far as the average rifle goes. The 9 minute vid (is it me or is it my rifle) is a good example of this, looking at the fundamentals only, no prep other than resizing the brass (it came from another rifle with a larger chamber), a quick fire form session then into it, studying basic factors.


We are a small, family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing, and rifle accurizing.