Home Forums Reloading Big Game Rifles Neck sizing and seating .308 brass with .300 SAUM dies

I have .308 dies and two .308 rifles. I was thinking of using a spare set of .300 SAUM dies for neck sizing and seating bullets for one .308 rifle instead of constantly adjusting from full-length sizing and seating with a different projectile in one rifle to neck-sizing and seating at a different length in the other by using the .300 SAUM dies for one rifle and the .308 dies for the other. Can anyone see any potential problems with this? Thanks.

Bad runout seems likely.

Are die adjustments really that hard?

Not hard, just a pain. It would be good to have the two different dies set up for each rifle.

I load for nearly a dozen 308 rifles and I guess I just don't see the problem.

Why would the runout occur more than with .308 dies (when neck sizing) when neck-sizing only with the .300 SAUM dies?

That depends on what 308 dies you're neck sizing with. Conventional neck sizing dies generally aren't the best for runout because they usually size the neck tighter than necessary while also not supporting the case body for alignment. The SAUM die will be no better in the first aspect, and even worse in the second.

As the die doesn't support the case body in either the .308 or .300 SAUM dies, wouldn't they give the same result when neck-sizing?

It's hard to say how bad much looser is compared to sort of loose. Conventional neck dies, even "proper" ones, aren't usually the best for runout.

Last week I inadvertently grabbed my Forster BR .308 Win seating die to load some 260 Rem cartridges. I was checking with a Sinclair gauge, averaging about 0.001" TIR. About half way thru I noticed I had the wrong die. It was an eye opener for sure. All cases were sized with an LCD (i.e. neck sized)

Spend a few bucks and get a neck sizing die, you`ll save a lot of BS and get better ammo.

FWIW, I neck sized a lot of my 308 comp. ammo in the day...can`t say it was helpful, so went back to full length sizing. YMMV.

These are both hunting rifles. The reason I neck-size is because there seems to be less case stretching, and I am happy with the resulting accuracy.

If you're going to neck size then get a Lee collet die.