How does one prevent bullet setback in gas guns when loading precision ammo? Take 6mm ARC in an AR-15. I only crimp blaster .223 ammo for AR-15s. I use Redding S bushing dies to size necks to .001” or .002” on bolt rifles. Do you increase neck tension with a smaller bushing for gas guns?
- Thread starter Lone star Shooter
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At present I only shoot gas guns and I've never had a problem one. Eventually I will get into the bolt gun world but it's up the road a bit.
I guess the only way to really check if it's a problem is to chamber a round and then eject it to see if the bullet has moved. Like I said, I've never had a problem one. Not saying it can't happen. I am just saying it hasn't happened. I am not crimping anything. .002 neck tension and no problem.
How much should the neck be under sized vs bullet diameter?
I also keep a Lee factory crimp die (no other crimp die) around for gasser... it's a collet and you essentially add neck tension after the bullet is seated
as for how much... that depends (I know, shitty answer), on a gasser, I like to start w/ .003, meaning that the neck of the brass grows .003 from sized and ready to load, to after a bullet is seated
as for how much... that depends (I know, shitty answer), on a gasser, I like to start w/ .003, meaning that the neck of the brass grows .003 from sized and ready to load, to after a bullet is seated
On 6.5cm .002 seems to work fine. But to be honest I haven't tested it and wont unless there is a problem. I just shoot.
I used to crimp 223, and 300blk for sa gassers.
I started to use mandrells -0.002 nt on them after fls.
My groups improved and differences between headstamps were way less.
My 6.5g rounds still being tested but don't seem to mind.
I have not measured after chambering since group size shrank accross the board.
Bolt guns included.
I started to use mandrells -0.002 nt on them after fls.
My groups improved and differences between headstamps were way less.
My 6.5g rounds still being tested but don't seem to mind.
I have not measured after chambering since group size shrank accross the board.
Bolt guns included.
0.003-0.004 neck tension is sufficient. Beyond about 0.004, you exceed the elastic limit of the case neck, and the bullet acts like an expander ball during seating.
Crimping is really only necessary for pistol rounds, to reverse the belling of the case mouth.
I would imagine that the opposite of setback could happen with the cartridge coming to a sudden stop once in battery. Kind of like an inertial bullet puller.
I solved this by incremental testing.
Resize, seat bullet, measure COAL, load by letting the bolt cycle, extract and measure COAL.
If it grew I resized with a smaller bushing.
Did this until the bullet didn't move. It only took .003 tighter to lock the bullet in.
For my set up this produced more consistent groups and velocities.
Downside is I have to use same brand of brass as different neck thickness will yield different tension.
Resize, seat bullet, measure COAL, load by letting the bolt cycle, extract and measure COAL.
If it grew I resized with a smaller bushing.
Did this until the bullet didn't move. It only took .003 tighter to lock the bullet in.
For my set up this produced more consistent groups and velocities.
Downside is I have to use same brand of brass as different neck thickness will yield different tension.
Thats why I went to a mandrell, same neck tension on all.
If you need 0.003 maybe you can order it I have only seen 0.001 and 0.002. Polishing a thousands off also should not be hard I do it on the expander buttons.
I used to crimp all rifle auto loaders but my accuracy went up when I stopped.
If you need 0.003 maybe you can order it I have only seen 0.001 and 0.002. Polishing a thousands off also should not be hard I do it on the expander buttons.
I used to crimp all rifle auto loaders but my accuracy went up when I stopped.
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