308 Reloading Help!!!

[GOING FOR 2000]

New Rem 700P 50 rounds down the barrel.

Lapua Brass 2nd loading, neck sized, trimed to 2.005, 42.8 Gn. Reloader-15, 175 Gn. SMK, CCI-200 primers, no crimp. Ogive seated 2.080,(bolt face to rifling 2.279), (2625 FPS over chorono).

I Know it is a long jump but but this weapon likes it. My original 700P was holding a 10" group at 1000 before the throat lost .037 at 819 rds. Rem. replaced this rifle under warranty.

The last 10 cases shrank .005 to 2.000 I never had a case shrink before. Grow yes shrink no anyone have any ideas why???

 

[Suasponte]

Re: 308 Reloading Help!!!

Are you having trouble chambering the rounds?

Have you checked your rifles headspace?

Maybe check your max trim length too!

Terry

 

[308sako]

Re: 308 Reloading Help!!!

!

 

[GOING FOR 2000]

Re: 308 Reloading Help!!!

Rounds chamber as proper no problems.

These cases are neck sized so head space is not an issue as the cases are fire formed to the chamber.
The headspace is within spec.

Bolt face to rifling is 2.268

Case chamber dimension is 2.044. Sinclair guage. My trim is 2.005

The shrinking has just started to occur previous cases have grown .002 to.003 in length.

 

[GOING FOR 2000]

Re: 308 Reloading Help!!!

I only neck size to eliminate head space and as much chamber expansion as possible.

Brass is fire formed to the chamber. Neck should increase in length not shrink. As it is the only un-restricted dimension.

Why would this start to occur in just the last 10 rounds?

 

[Sigarmed 1]

Re: 308 Reloading Help!!!

Shrinkage....Hmmmm...Was it really cold outside?

(Sorry couldn't resist)

Seriously though, I haven't been reloading that long but I have yet to see a case shrink. Mine always stretch .002-.003 like you stated yours "were" doing. Interesting...

 

[Rafael]

Re: 308 Reloading Help!!!

It is likely just some variance in the before and after measuring tools/technique.

Did you make sure the tool you used to measure was zeroed before both readings? What kind of tool did you use?

Also, were the cases primed for the "before" measurement?
If so, you may want to make sure you are seating the primers fully.

Also......yeah, still rambling.

Since this is a fairly mild load.....let's say there was zero growth to this load.
If you fire a neck of a certain diameter and it gains diameter in firing....it will lose some length as it expands. Neck size them and see what they measure then. The larger the variance between sized diameter and fired diamter, the more it could lose length.

 

[ranger1183]

Re: 308 Reloading Help!!!

the only time I've seen such a thing is with primers that protruded just a thou or two because I didn't seat them properly. Then when I fired them, the hot load FLATTENED the brass base perfectly evenly. When I did it, the brass didn't shrink, the primers were shoved in flush.

good luck.

 

[GOING FOR 2000]

Re: 308 Reloading Help!!!

Digital caliper for measuring.

Measured after firing, caliper on case not primer.

Measured again before priming.

Primers seated below case surface.

Cases only neck sized fit the chamber like a glove.

 

[DaddyRat]

Re: 308 Reloading Help!!!

Just a thought.

Have you checked the zero on the caliper? I had a caliper get out of zero one time and screwed all my measures up until I caught the problem.

 

[GOING FOR 2000]

Re: 308 Reloading Help!!!

The caliper has a zero button. I check and zero it every time.

I have totally run out of ideas and have done everything everyone has mentioned. This is really frustrating.

 

[Kogapsp]

Re: 308 Reloading Help!!!

Use an RCBS case mic and check with 0 head space gauge then mark the mic with what zero is. This check sized case to fired case then compare. case should be sized down .001.5-0020 . If is shinks from there I would check the bolt lugs for gullingor a build up of brass on the lugs. Check this to find out if this is the problem.

kn

 

[GOING FOR 2000]

Re: 308 Reloading Help!!!

At 75 rds the case shrinking problem stopped have no idea why but I'm not going to worry about it.

Moved the 175 Gn bullet out .008 now holding a 5 shot group that can be covered with a dime. I'm happy.

Now it's back to 1000 yds.