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I have a loaded case giving me neck OD of 0.336. If I resize using 0.334 or 0.333 bushing then put case through a 0.307 expander mandrel am I sizing the neck down to give it a 2/3 thou worth of neck tension then expanding it to give it a 1thou case neck tension ?
Reloading 300NM with 30cal 230g atips
Forgive my naivety, all new to me!
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100 percent. My 7mm saum seating depth ladder test had jumps Atwell as diffrlerejt neck tension using the app mandrel from ozark.
I run the same projectiles through my norma mag also, I use a whidden neck bushing die.
You will get more precise neck tension if you outside trim the necks too. I skim the necks on all of mine before first firing to even them up. Even Lapua has 1-1.5 variation in neck thickness around the circumference. I just even that up taking as little off as I can then. As they are already expanded for neck turning, I just neck them down to give 2 thou tension. Just got a Whidden FL bushing die too but haven’t used it yet.
Cheers.
Sort of ....spring back of the brass will determine what ID it is......annealed brass will have less spring back and a lower tension than work hardened brass. Your mandrel will still be tight when you pull it back....that is the spring back tension. If it was 0.307" then the mandrel would be a push fit and I bet it is not.Quote:
Originally Posted by Guy
Generally annealed brass spring back will be approx 0.0005". Work hardened...depends on the hardness.
0.0015" interference fit is still OK .....in fact I would say better than 0.001"
The main reason a mandrel is used is the concensus that many have found you get 'less runout'. The seated bullet is straighter.
I have heard that about bushings not being as accurate as the mandrel, but from what I've been seeing on my lots of cases is that the case neck thickness variation produced more of an error than either method. The mandrel had about half the neck thickness error than the bushing by itself - which makes a lot of sense. Either way, the case neck thickness error in the large proportion of brands of brass is less than 2 thou runout from what I have seen and brands like Lapua and Norma are generally well under that. If it's a standard hunting rifle there's more error in the thing than a thou or so of runout (but it probably makes you feel better knowing it's not there).