Load changed on 2nd firing

[timelinex]

So I finally worked up a GREAT load on my 338 with lapua brass. Great numbers,great groups, great performance down long range. Since I have 200 pieces of new lapua, and only have about 50 left, I decided it was time to make sure the 2ns firing doesn't change anything.

I neck size the brass (no tension going in so no need for FS), and go back to the range with my chrono. First I do 2 groups of the load with 'new' brass and I get 1/2 minute groups with great velocity spread. Then my next 3 groups are using the 1x fired brass, one group at the same charge, one group .2gr lower and one .2gr higher.

All the groups are >1moa and the velocities are slower. The same charge is about 25fps slower, and the .2gr higher charge is about 10fps slower. AHHHHHH. Back to the drawing board.

I have heard before that when someone uses a different lot of something and it changes the accuracy, they just bring the velocities to match the old lot and accuracy goes back to normal.

Is there truth to this? I'm really hoping I don't need to do a new workup.

 

[Captain Kirk]

Re: Load changed on 2nd firing

Try .2gr above your higher charge, your fireformed cases are now a "cast" of your chamber and have more internal volume than new, larger case equals less pressure and there is your lower velocity. You may also want to play with the neck tension if you have bushing dies, one thing at a time so your not chassing a ghost, your not too far off duplicating that magical load.

Kirk R

 

[milo 2.0]

Re: Load changed on 2nd firing

I'm here to the rescue again TL.

I've always been under the assumption that the 2nd firing very well could produce more velocity and pressure. Given the fact that you neck sized, no energy is wasted blowing the brass out to chamber specs. All the energy is going out the barrel.
Was it cooler today? Was DA the same?

At 10fps, I'd think chrono might be suspect.
Good luck!

 

[timelinex]

Re: Load changed on 2nd firing

I loaded examples with the 'new' brass, specifically to rule out differences in loading technique or outside temperature etc..

If it was just velocity, I wouldn't care. There was a clear diff in groups.

Anyways, I'm loading a couple more at higher charges as well. I caught another difference as well between the loadings, so maybe that is what made the difference. The same setting on the seating die produces 2 different depths(by .8), between the new brass and 1x fired. Perhaps that was the problem.

 

[Boltfluter]

Re: Load changed on 2nd firing

I would check the bullet run out in new cases versus the reloaded ones to rule out that your dies might be inducing something. Just a thought.

Regards,Paul

 

[timelinex]

Re: Load changed on 2nd firing

You know what, screw it.. I'll think I'll just move to full sizing em. I will eventually have to FS anyways, and that means I will have to retest everything AGAIN.

Can I just run my loaded ammo over a body die, or should I take all of them apart and use those 9 rounds as foulers? Its not a compressed charge, so it should 'squeeze' any of the powder in there.

Thanks

 

[timelinex]

Re: Load changed on 2nd firing

Full sized all my cases, sat the bullets out farther to match the same OAL between the new brass and 1x fired, and the load stayed the same. Same velocity and same POI at 100 yds. Great.