Neck down Lapua 308 to 7mm08?

[JBomb]

I'm debating building a 7mm08 using the AI AW magazines. I was wondering if anyone had experience using the lapua 308 brass and necking down. It seems the shoulder would be a little off per cartridge diagrams? Did you have fireform the cases to the chamber?

Kind regards,
Jared

 

[turbo54]

Re: Neck down Lapua 308 to 7mm08?

The trouble with doing this is the thickness of the case walls of Lapua brass taper all the way from casehead to neck...meaning the shoulder is thicker than the neck.

This will cause the caseneck to thicken, and probably become too thick for your chamber - that is, unless you have a rather loose SAAMI(+) chamber.

I did a lot of load workup/experimenting with my buddies 708, which has a SAAMI minimum chamber, and both Federal and Winchester 308 brass when necked down, were too thick, and there was not adequate neck clearance.

 

[shoot4fun]

Re: Neck down Lapua 308 to 7mm08?

Best results I had was necking up Lapua 260 with an expander die. I did a cleanup on the necks with a neck turner. I had great results this way and no donuts to deal with.

 

[JBomb]

Re: Neck down Lapua 308 to 7mm08?

Would the neck have to be turned? Would that eliminate the neck tension issue?

Kind regards,
Jared

 

[former naval person]

Re: Neck down Lapua 308 to 7mm08?

Maybe. You would have to measure the brass and the loaded brass and the fired brass to be sure. I think you would have to fire a round of factory 7mm in the new chamber and measure it. Then...neck down a .308 Lapua and measure it with a bullet seated. If less by .002 or so, then you are good to go. If the loaded 7mm/.308 is at the same or greater than the fired brass, then you'll need to ream or turn. If you are building a rifle, then just size the Lapua brass from .308 to 7mm, seat a bullet or two, and measure the neck. What ever it is, add .002 to it and tell the gunsmith to make the neck of the chamber XXX/ then you won't have to do anything except load and fire. You may need to have your dies dimensioned...Forster does that for $15 including return mail. JMHO

 

[Nortex]

Re: Neck down Lapua 308 to 7mm08?

Why not just use the Winchester 7mm-08, as their brass is fairly decent.

 

[JBomb]

Re: Neck down Lapua 308 to 7mm08?

Thanks for the comments guys!

I just thought Lapua brass would hold up better, although I have never used the Winchester Brass.

Originally, I thought about going with the 6.5 Creedmoor, but with only one supplier of brass...I'm rethinking that option.

Kind regards,
Jared

 

[shoot4fun]

Re: Neck down Lapua 308 to 7mm08?

Maybe only one supplier of brass but it is very good brass. I have gotten surprisingly good life from my 6.5CM at max velocities.
BTW, the suggestion to use WW brass may not be a bad one. I have used it too and found it to be very good brass. Accuracy has certainly not suffered and I don't feel so bad when I have to toss one.

 

[gcoulsey]

Re: Neck down Lapua 308 to 7mm08?

I'm in a similar position to the OP, but I'm committed to .308 lap brass already.
I have x700 once fired that I'm about to start prepping for the return of my rifle next week.

based on my measurements so far, I'm expecting my sized down rounds to end up at .316" (average) outside diameter once I get the bullets seated.. And it appears SAAMI minimum chamber dimension is .316" ...

neck turning isn't a problem, I have all the tools for .30 cal already,
My questions are..

1. To save buying a new expander/case pilot for 7mm, I'm going to turn the necks BEFORE sizing them down..do I turn the entire length of the neck and slightly into the shoulder junction as normal?

2. how much chamber clearance around the neck is desirable for bullet release?
Is .002" enough? (assuming my chamber happens to be saami minimum)

Thanks, Giles.