308 to 7-08

rmarshall · Feb 10, 2014

I have taken 300 WSM and run them through my 270 WSM dies and never had a lick of trouble, they turn out perfect, how come when I run 308 win through the 7-08 full length they are giving me the little donut or ring at the bottom of the next, it's just slight, I understand different brass thickness and so form, would they be fine to fire and form more perfectly to the chamber, is there a cheap way to decrease the thickness of the 308 necks if that is the problem. Only done a few brass. maybe I should just sell the 308 brass and buy some ammo since I can hardly find brass without paying an arm and leg. The brass are HSM 308 brass and they are annealed. If that will help-thanks

Songdog · Feb 10, 2014

Pics would really help us help you.

kraky · Feb 10, 2014

Reminds me of a mini version of what I see converting 3030 to 7-30 waters. My rings are far more pronounced. I'll bet a 12 pack you load em up and shoot em and the ring goes away never to be seen again. And accuracy will be fine when you fire form.
If they chamber..load up a medium load and give it a go.

rmarshall · Feb 10, 2014

Kraky, I did load one medium load or so and shot it, it looks much better, still visible somewhat. I was just thinking they won't last as long. Saw no signs of pressure or any tight loading. Thanks for the reply

kraky · Feb 10, 2014

I just looked at some ammo I downsized from 308-708 and can sort of see a little of what you got on mine but not as much. When you downsize 308-708 the neck of the 308 becomes part of the shoulder of the 708.
I wonder if being annealed is making that happen a little more pronounced on your brass?
I still don't think there is anything about your brass that will shorten life.
One warning though...your 708 necks are now ever so slightly thicker than they were as 308. Be sure you are getting safe bullet release from the new brass.

Songdog · Feb 10, 2014

Die screwed in too far.

Raise your press to the top (assuming it doesn't cam over)
Screw die in until it stops against shell holder
Screw back die out 1/4 to 1/2 turn
Color case neck with a sharpie
Run case into die
See where case neck is sized too
Screw sizer down a little
Run case into die again
Repeat until desired headspace

Or...

A little too much lube can do weird things too...

kraky · Feb 10, 2014

The oversizing idea is pretty valid. I now use a hornady head space checker to set my sizing die but in the old days tinkering w/the 7-30 waters did not.
If the shoulders on the 308 were blown out a few thousandths and along comes a 708 die trying to move shoulders and neck down perhaps funky things could appear?
I'm pretty sure in a perfect world the datum line on a 708 and 308 are a match...at least my rcbs 308 head space checker measures them the same.

dubyam · Feb 10, 2014

I've done the 7-30 conversion before, and while that looks somewhat like it, I see a couple of issues. First, there are multiple steps on that shoulder, instead of just two (the original shoulder/neck junction, and the new shoulder/neck junction). On that case, there is a second bulge down near where the datum line should hit the shoulder. Faint, but visible. Second thing that sticks out to me is the belled case mouth. I don't bell any of my rifle rounds, and I'm wondering if whatever that case is bottoming against that bells the case mouth, isn't creating the third "ripple" in the shoulder? If you're belling, inspect prior to that step and see if that's where the additional bulge is coming from. If you're not, check out how your dies are set up (see Songdog's post) as well as checking your case length to be sure the necks are not overly long and clanging into the "end" of the sizing die internally.