AusVarmint

I'm looking at necking down .308 Lapua cases to 7mm using Redding bushing dies. I've been advised that I should use .309 -.311 bushings for standard 7mm-08 cases, but obviously with necking down from .308 the necks will be thicker. How can I find what size collet to get & how do I know if the sized neck is too tight when projectile is seated?
I don't have a neck trimmer.

On another board, it was recommended to neck up 243 lapua cases to avoid the neck thickening problem.

Yes thats true except that Lapua .243 brass won't be available for 6-8 weeks.

Vanders

I have no experience with 'necking down' and all I can imagine is problems ahead........without a turning tool I would wait for the brass

The usual method for bushing size is - measure the outside neck diameter of a loaded round and subtract 3 thou to = bushing size. You can vary the neck tension to 'tune' by going up or down in bushes. I am unsure if you would get down from 30 to 7mm with a bush in one pass as they are not very tapered.....¿

As to wether it fits or not, you need to now your chamber specs, there is a product called Cerrosafe ...I think anyway.....that's a low melting point alloy, you simply plug the throat and pour it in. when set you have a 'cast. of your chamber to measure. Be very carefull...remember there needs to be room for the case to 'let go' of the pill on firing.

Hopefully somebody else with experience of 7/08's will chime in

KY

If one emails Lapua, they will tell you that their strongest brass and that which will sustain the most reloads at their given test pressure, is 6BR or 308. Why use 243 when it IS inferior to the 308 in both measurement and reliability? I have never split cases sizing down, but have done so sizing up. A Lapua 308 case sized down to 7 mm with a pill seated measures .316" across the neck. This may be too large for some factory chambers or just perfect for neck turning if one has the gear. SAAMI specs for a chamber is .318" across the neck. Not all factory chambers are this size as most i have encountered are usually smaller

Thanks Tony, so if its .316 for example across the neck, then using a .314 bush would be recomended. Is this correct?