Re: Cornmeal forming bad on a new barrel??
If you go with a longer neck than that of the 338 Lapua, turning the necks before you fire form them will yield less than satisfactory results IMHO, especially if you have a tight neck chamber. Inconsistant neck thickness the length of the neck is what you'll likely end up with.
The 338 Lapua shoulder ends up being IN the neck on your new cartridge, and leaves a smaller outside diameter "ring" at the new junction on top of this, so the neck looks like a wave when looking down into it. No mandrel will remove it, and it has to be hammered out by pressure. IF you're LUCKY, you might be able to turn and ream the high spots after running them through the sizer die and end up consistant, IF the low spots inside and out turn out to be higher than the amount you're cutting inside and out.
Clear as mud?
I would go with a .375" neck length on the 7mm, .400" seems about perfect for the 30, and maybe .425" on the 338's.
The throat errosion on my 30-338 here is so little it's almost too good to be true, but fire forming with COW after FL sizing the virgin stuff, I would consider necessary for a good neck turning job.
Moving the shoulder forward will leave you with a short neck, and I believe throat errosion will be greatly accelerated, but you WILL be able to turn the stuff and not have to form with COW first. I would might go this route on a 338, 416 or something larger having this case volume, but no way I'd do it on a 30 or smaller with what I've learned now... One reason I don't particularly care for the 300 and smaller Ultra Mags, short necks...
My 2 cents. [img]images/icons/smile.gif[/img]