If you are necking down 308win brass to 7-08 then I would measure the distance on a std 7-08 case from the base of the case to the shoulder- neck junction using calipers. This is how far you should neck down 308win brass to 7-08. I believe the 308win case is slightly shorter in this measurement so you will have a slight bulge or second shoulder right above your shoulder-neck junction on your necked-down 308win case. It should chamber and headspace on this slight bulge, if not neck down slightly more until it does with slight bolt resistance. After fire-forming, the new 40deg shoulder will eliminate this slight bulge. Be sure your new Ackley Imp. loads do not fit too tight in the chamber due to the increased neck diameter of the necked down 308brass. You want at least .002-.003 clearance for adequate bullet release in a hunting rifle. I neck-turn slightly as a last step in the process with necked- down 308brass. I believe the std neck diameter for the 7-08 is .318, check with who chambered your rifle for reamer specs to play it safe. sure-shot
I wouldn't form 7mm-08 AI OR 7mm-08 standard from 308 brass. 308 brass is 0.020 shorter than 7mm-08 and if you reshape the shoulder or the taper of the case it will shorten up even more. Buy 7mm-08 brass and fireform. 308 is 2.015 long and 243 Win and 7mm-08 is 2.035 long, standard.
Usually when you neck down the case length grows, the more smaller you go the longer the case gets and but going down 0.024 won't get you 0.020 more length.
I just finished making 50 - 22-243 cases from 308 Fed Gold Metal cases and I didn't get any more length, they ended up 2.010 after trimming to the shortest case. I usually use 243 brass and neck down in one pass and most of the time end up with cases about 2.045 long which lets me trim to fit my chamber and get the longest neck I can, but I wanted to try the Fed GM to see how good it was.
Think I might try some of that high priced Lapua 243 at 43 bucks a hundred and not have to mess with all the other stuff.
The shorter case length mentioned might make a difference in accuracy and in some rifles won't affect accuracy at all. It will eliminate case trimming chores for awhile though. sure-shot
I didn't trim to such a short length on purpose Sure-Shot, it just came out that way, but you're right I won't have to trim for a LONG time. I usually just use Win 243 cases or whats on sale, and trim to whatever the shortest is, usually around 2.035 to 2.037.
I was just experimenting while the snow's on the mountain and in my yard.
I even made some cases from 6mm BR brass to do the small primer thing and get all the length I could. I ended up at 2.075" OAL with a neck around 0.300" long. Finally got to seat those pipsqueak Rem 45 grainers out to touch the lands, 40 gr weren't out for another 15 years. As I remember I got a lot of hang fires, patterns instead of groups and lots of copper plating in the barrel.
Very strange sounds came out that barrel when one did go off. Somewhere between a scream and a shriek. Make me grab for ol' slabsides and turn around real quick with my back all humped up. Another one of those learning experiences I wouldn't give up for the world, but I tossed the cases and waved a cross over them just for sure.
Why not just fireform some 7mmX08 ammo in your rifle? Load and shoot. Then you will have once fired brass ready to load. That's what I do with my K-Hornet. If you don't want to spend the bucks on the factory ammo, how about loading some from new 7mmX08 brass?
The reason I wanted to use 308 brass was I figured I could buy premium in that calibre.Also I didn't want to overwork brass necking up and then down.From what I have read headspacing on the bullet won't have enough tension to fireform case so I figured use the 308 neck down to second shoulder to hold case during fireforming and lube case?What do you think?I guess if my reg 7mm-08 brass is a crush fit in the chanber it would probably be O.K.I will fing out case length and outside neck dia. for my rifle. Thanks to all W.E.
Just a little info here, in Wildcats Combo I&II, Layne Simpson used 308win brass for his 7-08AI(7SGLC). No factory 7-08 brass avail back then, he did state the necks were short but no problems. He only trimmed once during 20 loadings of same cases. sure-shot
sure-shot
