Enlarging the Flash Hole?

[steve4102]

I'm loading for the 6.5 Grendel using Alexander Arms(Lapua) brass. The flash hole on this brass is small, really small. I'm also trying to work up a load with AA 2520, a very fine ball powder with 120gr bullets.

With standard 7 1/2 primers my velocities are all over the place. When I get really bad ES like this I usually switch to a Mag primer and work my loads up again. Sometimes it works and sometimes it doesn't. My problem is, nobody around here has ant SR Mag primers.

Then I thought about the small flash hole. What do you think will happen if I open up the flash hole to normal? Do you think this will help reduce my ES with non mag primers or will it just ruin my 6.5 Grendel brass?

Thanks
Steve

 

[627PCFan]

You remove material from the base, you weaken the brass. Also might advance the burn cycle beyond the correct speed??

 

[loadedround]

Don't you think that the brass manufacturer made their flash hole a certain size for a particular reason. Don't do it.

 

[243winxb]

Flash Holes
Quote:
Most commercial cartridge manufacturers specify a 0.082" flash hole diameter. There are an increasing number of manufacturers using a 0.058" to 0.062" flash hole on some of the target cases such as the PPC, 6BR, and 223 Remington. If you are checking the .082" flash holes, use a #45 wire size drill bit as a gage.
http://www.sinclairintl.com/newsletters/99b1.html << Old link, but thats where info came from. New Link might help> http://www.benchrest.com/forums/archive/index.php?t-41950.html

 

[rcmodel]

my velocities are all over the place. When I get really bad ES like this

Well, it sounds like you have a chronograph and know how to use it.

So, if I were me, I would sacrifice 10 cases and drill out the flash holes to .082" and test them for velocity, ES, and accuracy change.

If it works, or doesn't change anything at all, then I would drill them all out.
At least I wouldn't have decapper pins getting stuck in the holes.

If ultimate extreme accuracy is the goal, I doubt switching to Mag primers will help. I think it will probably hurt.
Standard BR primers might be the way to go.

BTW: It will not weaken the brass.

rc

 

[Deavis]

You remove material from the base, you weaken the brass.

You mean the flash hole that is already sitting above an enormous hole called the primer pocket? Just off the cuff, it would seem that biggest danger in enlarging the flash hole would probably be excess transfer of pressure back to the primer rather than making the case head weaker, i.e. increasing the bearing area of the pressure, not raising the pressure. The case head is, for all intents and purposes, already "weak" there by removing material for the primer. It strength would not be significantly compromised by removing the entire flash hole and boring the primer pocket all the way through, no different than a pipe where the outer diameter provides most of the strength of the pipe and the center almost nothing. However, that is addressing bending force and in this case there should be none so it is of no consequence to the case head for strength since it is a small component, especially in the Z-axis (bore) pressure.

The fact that it is filled in with the primer is of little consequence since the pressure of firing will unseat the primer until the brass is fully pressed against the breechface and reseats it flush. My concern would be that you shove it out and deform it before the brass catches up with it after obturation.

 

[rcmodel]

Well, it doesn't outrun the pressure curve on a gazillion other calibers with standard size .082" flash holes so I doubt it would on a 6.5 Grendel either.

rc

 

[Deavis]

No doubt. My concern was mostly theoretical addressing what I think we both see as a non-existent problem. I think it would be interesting to see how an overly large flash hole, I mean almost the diameter of the primer, and a compressed flattened ball powder in a large cartridge changes ignition and the pressure curve. Interesting exercise.

 

[Walkalong]

The most accurate caliber in the world, by one standard at least, uses .062 flash holes, but then again, it has less capacity than the 6.5 Grendel as well.

Try rcmodels suggestion.