338LM Bullet Setback

[Redhook]

I’m loading new Lapua Brass in pretty much a standard configuration. 250gr Scenar over 89.8gr of H4831SC. I’m clocking these at 2925fps. I’ve just been testing loads up until now and have been single loading these for fear of setback affecting my tests.

So, now that I’ve found my loads, I’ve just started loading the magazines up. First round out I’ve got anywhere from .002” to .010” set back on the rounds in the mag. Seems like they got worse the further down in the mag they were. Obviously I stopped and went back to single loading for the rest of the day.

Has anyone else experienced the same problem? Again, these are factory new brass that hasn’t been resized yet. So, maybe the neck tension needs to be increased. Should I neck size them first? I have both the redding bushings that will take .002” and .003” off.

Since, I’m on the subject, when you guys neck size, are you using the expander ball? Seems counter productive to pull the ball through there once the neck has been sized using the bushing.

 

[MitchAlsup]

Re: 338LM Bullet Setback

A) I would try the 0.002 bushing first and see if you continue to get setback--if so, advance to the 0.003.

B) With a bushing neck die you should not be using the expander ball.

C) Before priming and powdering the cases, verify that you do not need to push the sholder(s) back. you can use you gun to do this, you can use an RCBS case mic, a case gauge, or a stoneypoint (n.e. Hornady) tool.

 

[esromvre]

Re: 338LM Bullet Setback

Both FL and Neck sizers size lower than what you want for tension. however; If you have the right size bushing for your chamber you do not need the ball.

Neck thickness times 2 plus .338 minus .002 to .004 and you are good.


I am not shure what you are asking on the setback though.
If its what I am thinking you mean could be the anneiling on the brass.
Are the necks turned?

I am sure that others on here will also be able to help. Most people here are full of knolage.

 

[Winchester 69]

Re: 338LM Bullet Setback

My assessment is that while case constriction is part of the friction equation, another is surface area. If you're loading unsized brass, then the brass effectively isn't round, and the constriction on the surface area isn't uniform. The most important element in truing the brass is to pass an expander of some type through the neck. I would suggest sizing with the expander in place on new brass. Then you will have the complete surface area acted on by uniform tension. The tension can then be increased if necessary. Unless the neck is dented, subsequent resizing can be performed without the expander.