.243 and .308 sized to 7MM-08, does it make a difference?

bsmith · Nov 15, 2007

I have a lot of .243 brass and my dad has a ton of .308 brass. I'd like to resize some of it to fit the 7MM-08 that will be here next week. Is it better to neck up or down? Does it make a difference? Will the .308 end up too short?

rick smith · Nov 15, 2007

Neck thickness would be the main difference.Rick.

2ndtimer · Nov 15, 2007

Anytime you neck brass down, you have the possibility of case necks thickening, which can increase pressure. If the necks become too thick, the bullet won't be properly released, hence the increase in pressure. It may may then be necessary to turn the case necks to make sure you have sufficient clearance for the proper release. Necking cases up may slightly thin the necks which could lead to premature neck splits, which may not be conducive to great accuracy, but at least isn't overly dangerous. I didn't seem to get as good accuracy with necked up .243 brass when I loaded for a 7mm-08. Buying factory 7mm-08 brass seemed to be the best way to get top results. I didn't really try necking down .308 brass, but the one or two I did attempt seemed to have have thicker necks, so I didn't use them.