mrawesome22
New member
Bart, I did mention it. So did many other posts with bump included in the search terms.
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"Bumping" the Shoulder Back
- Thread starter jason75979
- Start date
mrawesome22, yes you did mention it. I just learned that by rereading some. I must have got that impression from another thread. Sorry 'bout that.
The big advantage of using a shell holder of the correct height and setting up the die correctly is case headspace can be held at very narrow tolerances; .001" for example. It's almost impossible to be that consistant with any other method because of press springback and inconsistant amount of lube on the case.
The big advantage of using a shell holder of the correct height and setting up the die correctly is case headspace can be held at very narrow tolerances; .001" for example. It's almost impossible to be that consistant with any other method because of press springback and inconsistant amount of lube on the case.
I have another question. I am using the neck sizing die, and it has been said that the cases will eventually become hard to chamber and then need to be full length sized. When this happens, could I not just set up the die as mentioned and bump the shoulder back .002? I am thinking of buying the RCBS Precision Die but want to be sure that it will work for my purposes.
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Yes, the shoulder needs to be set back sometimes. But there's another interference spot that causes accuracy problems.
Neither cases nor chambers are perfectly round. They're all out of round some small amount; they're egg or oval shaped. Multiple firings on a neck only sized case gets its body diameters closer to the chamber diameters. When the small diameter of each match each other, there's a slight, often unfelt binding or slightly harder bolt closing. This interference causes accuracy problems. In some instances, the interference at the shoulder-body junction tends to put the neck/bullet axis off center in the chamber. And neck only sizing sometimes puts the neck axis off center of the shoulder axis because nothing's supporting the case body when the neck's sized down.
If you full length size the fired case every time its fired and set its shoulder back a couple thousandths, this interference situation will never happen. The front of full length sized bottleneck cases whose shoulder is set back a bit always centers perfectly at the front of the chamber before the round fires. This is why Sierra Bullets full length sizes all their cases used to test there product for accuracy. They tried neck only, partial neck and all sorts of in between combinations back in the 50's. They've been full length sizing all their test cases since then. Their best lots of match bullets made with perfect jacket material shoot 10-shot test groups in the 1's; that's under 2/10th MOA.
Neither cases nor chambers are perfectly round. They're all out of round some small amount; they're egg or oval shaped. Multiple firings on a neck only sized case gets its body diameters closer to the chamber diameters. When the small diameter of each match each other, there's a slight, often unfelt binding or slightly harder bolt closing. This interference causes accuracy problems. In some instances, the interference at the shoulder-body junction tends to put the neck/bullet axis off center in the chamber. And neck only sizing sometimes puts the neck axis off center of the shoulder axis because nothing's supporting the case body when the neck's sized down.
If you full length size the fired case every time its fired and set its shoulder back a couple thousandths, this interference situation will never happen. The front of full length sized bottleneck cases whose shoulder is set back a bit always centers perfectly at the front of the chamber before the round fires. This is why Sierra Bullets full length sizes all their cases used to test there product for accuracy. They tried neck only, partial neck and all sorts of in between combinations back in the 50's. They've been full length sizing all their test cases since then. Their best lots of match bullets made with perfect jacket material shoot 10-shot test groups in the 1's; that's under 2/10th MOA.
Yes. Even w/ neck-size-only bushing dies, brass flow will eventually shove the shoulder forward enough that intermitant "bump-back" is needed.been said that the cases will eventually become hard to chamber and then need to be full length sized. When this happens, could I not just set up the die as mentioned and bump the shoulder back .002?
A standard full-length resizing die will work just fine for that.
Quote:
been said that the cases will eventually become hard to chamber and then need to be full length sized. When this happens, could I not just set up the die as mentioned and bump the shoulder back .002?
Yes. Even w/ neck-size-only bushing dies, brass flow will eventually shove the shoulder forward enough that intermitant "bump-back" is needed.
A standard full-length resizing die will work just fine for that.
If you believe a case can be fired, as they say 'fire formed' then neck sized 5 times, then after having been fired 6 times a case can be full length sized to minimum length/full length sized???? No, after my cases have been fired 6 times they are what others call full grown??? and stiff as a board and are brittle with jump back, pop back or spring back, the 6 time fired case offers resistance to sizing, after a case has been fired 6 times try screwing the die in an additional wild 'guestimate' of a turn like one, or add 'annealing' to your vocabulary.
F. Guffey
been said that the cases will eventually become hard to chamber and then need to be full length sized. When this happens, could I not just set up the die as mentioned and bump the shoulder back .002?
Yes. Even w/ neck-size-only bushing dies, brass flow will eventually shove the shoulder forward enough that intermitant "bump-back" is needed.
A standard full-length resizing die will work just fine for that.
If you believe a case can be fired, as they say 'fire formed' then neck sized 5 times, then after having been fired 6 times a case can be full length sized to minimum length/full length sized???? No, after my cases have been fired 6 times they are what others call full grown??? and stiff as a board and are brittle with jump back, pop back or spring back, the 6 time fired case offers resistance to sizing, after a case has been fired 6 times try screwing the die in an additional wild 'guestimate' of a turn like one, or add 'annealing' to your vocabulary.
F. Guffey
confirmed shooter
New member
bumping
when bumping, that brass must go somwhere. Usually where it dosnt belong. go with what the book says or change the bbl to a size you want. rifles usually shoot better when neck sized(bolt action) because the chamber is a coustom fit after firing. all cases stay with the parent fire-arm. this is different with semi-auto because of the neck crimp.
when bumping, that brass must go somwhere. Usually where it dosnt belong. go with what the book says or change the bbl to a size you want. rifles usually shoot better when neck sized(bolt action) because the chamber is a coustom fit after firing. all cases stay with the parent fire-arm. this is different with semi-auto because of the neck crimp.