Sizing die bushing

[jmcarrol]

I now have two 7mm Rem mags. I have always used regular master hunter Redding dies for the first one. I was looking at type S bushing die for the second and was wondering if anyone uses ADG brass with berger 180s and can recommend bushing size. Or should I load this combo up in my master hunter sizing die that I have and measure for the bushing for the new one?

 

[The Oregonian]

Typically it will be loaded brass at neck minus the desired neck tension...seems most go with .002 tension. That should give you the same answer as bullet diameter plus 2x neck thickness, again subtracting desired neck tension for the bushing.

 

[jmcarrol]

Anyone running a bushing die with ADG brass with 180 Berger's for 7mm rem mag? I loaded my combo through standard master hunter dies and get .311, so I guess I need .309. That seems to be one of the smallest options in the bushing kit I was looking at. What's a tighter bushing aka more neck thickness going to affect loads compared to say a .310?

 

[Mikecr]

You likely need a .309 bushing.
If you'll be sizing down more than 5thou, you should try a .310 bushing to mitigate excess sizing.

What happens is the bushing takes the neck down to .309,, on release the neck springs back outward to maybe .310 OD. That's not 'tension', but ~1thou of 'interference' fit. Tension is a matter of spring back force gripping an area of seated bullet bearing. We currently have no way to measure this, but we can adjust tension through annealing and sizing length.
Adequate interference is the amount that necks spring back from sizing. This is usually ~1/2thou, but 1thou is easy & doesn't hurt. Sizing down more really does nothing functional, as the seated bullet will just expand the neck right back up to counter that extra effort. So it's just excess sizing, and excess seating force.