Originally Posted by Mikecr
Forget what BR shooters do.
They don't shoot 270Wins in competition, and YOUR best neck tension would be determined by YOUR load development(not theirs).
I agree. You will not get better bullet seating concentricity by only sizing 1/8 in a standard neck clearance chamber. The BR shooters may do that because the neck is a tight neck chamber and it does not expand much so the amount of resizing is very minimal .
You can do a partial neck sizing operation in any standard factory chamber but you need to size down 3/4 of the length of the neck to make sure you have enough length to align the bullet and neck tension to hold it. A long neck case is good for this operation.
BR shooters gently feed one round at a time by hand it's a different situation to hunting and normal shooting using magazines etc. and big kickers .
Forget using a standard full length sizing die . Buy a Lee collet die and put a washer over the case on top of the shell holder this will shorten the length sized and allow a slight extra shoulder for better alignment.
If the extra shoulder makes chambering a bit tight , size down the neck lenght more until it chambers nice.
However a very slight crush as the bolt closes is ok as it usualy dissapears after first firing and you have a nice minmum headspace case. It varies with different chambers and case designs.
However to preserve this slight shoulder you need to buy a body die to size the remainder of the body .
Using a standard type die to partial neck size is always a risk that on extracting the case the friction may pull the shoulder out and prevent easy chambering .