Primer pocket flash hole variations

[Blitzfike]

I've been processing a variety of 308 and 7.62X51 brass for an upcoming shoot and since this was all from
someone elses rifles, I did the whole process. Size,Trim to length, swage out the military crimps on the
military brass, then tumble to get rid of the lube. As I take the cases out of the tumbler, I check the flash
holes on each to verify there is no media stuck in the flash hole. I then do the pocket uniformer thing to
get rid of any carbon and make the pockets uniformly deep. As I was looking at the cases I noticed that
there was a lot of variation in the flash hole size. Not just one brand of brass, but among all of it. I had to
uniform the flash holes as well. I use a Dillon pocket swage to remove the crimps, and its possible that I'm
pushing brass from the original punching back into the hole. I may have to machine an insert with a recess
in the end to avoid this. Has anyone else experienced this? Blitzfike

 

[MoBoost]

If you are worried about flashholes, use one of these: http://www.midwayusa.com/viewproduct/?productnumber=729748

P.S. Gotta spend $1/case to get some true uniform flash holes ... somewhat.

 

[Blitzfike]

That is basically what I'm using. Not that particular brand but the same tool.

 

[Fyrtwuck]

I use similar one made by Lyman and have it set up on my RCBS trim mate.

 

[HiredHand]

Any opinions on how much primer flashhole uniformity plays in accuracy?

 

[Blitzfike]

I haven't done any testing, but I would think that restricted flash holes would result in slower ignition
resulting in lower velocities. I will segregate some when I run across them again and see what the
chronograph shows between the restricted flash holes and non restricted. Good question.. Blitzfike

 

[ripnbst]

Part of me agrees with Blitz and part of me thinks that as long as you are using the same measure of powder AND all that powder at both rates is being burned before the round leaves the muzzle the velocity would be the same.

 

[MoBoost]

Once I get the load/brass ready - I can some real testing with 6PPC, I have both big and small flash hole small primer brass, and I can make some large primer brass too.

 

[HMFIC]

Once I get the load/brass ready - I can some real testing with 6PPC, I have both big and small flash hole small primer brass, and I can make some large primer brass too.

There isn't any doubt that you'll see velocity differences between big and small flash holes. It's an interesting test to see exactly what the difference will be in that scenario though.

Flash hole uniformity is about making sure that the primer pocket is flat, round and consistantly holds the primer in the same flat and even position relative to the flash hole. You want the primer to sit perfectly flat on the brass so it's not canted and that when the firing pin hits, it doesn't allow any movement from the strike either. Deburring is to make sure that you remove any burrs on the actual flash hole, the idea is to deburr without increasing the size of the flash hole. The whole set of actions is designed to get you a clean and consistant ignition.

It WILL make a difference if you're using brass that needs it done, but then again you have to be able to hold and read wind before you realize it.

 

[HMFIC]

I just fully read the OP now lol...

Ya consistant flash hole size across different types of brass can really be frustrating but I've always made my match loads with brass from the same batches, types, etc... so never really gave it much thought in that regard.

The nice thing is that once you do it once, you should be good to go. Describe the tool you're talking about making in more detail... are you wanting to deburr at the same time you uniform or just wanting to fill the flash hole so shavings from uniforming don't end up stuck in the hole?

Just buy some good Lapua brass for accuracy and then you don't have to worry about it as much... I had about 2000 once fired pieces at one time