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shoulder bumping

 
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  #1  
Old 07-23-2006, 09:25 AM
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Join Date: Feb 2006
Location: Nottingham, UK
Posts: 261
shoulder bumping

i have a 270 wsm minimum sammi speck nesika

on some of the cases (quite a few) after i have fired a shot
i get hard bolt lift,now this has happened when i was 1.7g under max and again now i am 4 tenths under max,it dose not happen on all of them but quite a few.
do i have to bump the shoulders back on them all every time i shoot the rifle,and dose anyone else have to do this.

135 SMK 65.3g n165 Norma brass no tern on the necks,primer pockets done,
this happened on fire forming as well,and i have now only shot the brass once

fire forming load was 65g H4831sc 135 SMK
i have checked my neck expansion and i am getting 3 thou


any thoughts
thanks
Colin
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  #2  
Old 07-23-2006, 10:37 AM
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Join Date: Dec 2005
Posts: 2,114
Re: shoulder bumping

I've had your same problem with binding bolts on opening them when the bolt face was quite a bit out of square and fired cases were neck sized, reloaded then oriented against the bolt when they were fired again. The angled surface of the case head when first fired would closely match the same angle of the bolt face. On cases first fired and had the greatest case headspace were the ones that usually made the bolt bind on opening.

When I full-length sized the fired cases setting the shoulder back a few thousandths of an inch the bolt binding problem went away. Of course when the bolt face was squared with the chamber axis bolt binding never happened for the most part. Sized or new cases with the same exact headspace will not have same headspace after firing; all cases don't expand and/or stretch exactly the same. The longest ones, when only neck sized, would sometimes cause bolt binding when fired again or twice in the same chamber with squared bolt face. This sometimes happens.
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Old 07-23-2006, 11:19 AM
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Location: Nottingham, UK
Posts: 261
Re: shoulder bumping

hi Bart b
so if i just bump the shoulders back they should be OK,
its just that i have never had to bump the shoulders back so early in the cases life.

when i was shooting the groups,if the cases went in to the chamber with out it feeling hard to close the bolt,they shot in to .3
3 shot group @ 100
if the bolt was hard to close they shot about 1/2" away,high and to the right,

did yours do this as well Bart?????

thanks Colin
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  #4  
Old 07-23-2006, 08:47 PM
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Join Date: Dec 2005
Posts: 2,114
Re: shoulder bumping

[ QUOTE ]
when i was shooting the groups,if the cases went in to the chamber with out it feeling hard to close the bolt,they shot in to .3 3 shot group @ 100 if the bolt was hard to close they shot about 1/2" away,high and to the right, did yours do this as well Bart?????

[/ QUOTE ]Yes; I've never got good accuracy from any tight fitting case in the chamber that requires more force to close the bolt than an empty chamber needs. There's several reasons why this happens but I believe they're all caused by different pressure points on the bolt face before the round's fired. Full-length sized cases with shoulders set back a bit have never had this problem and they've always shot more accurate. And I've got from 50 to over 80 reloads per case using normal maximum powder charges this way. Hot loads will shorten case life and usually accuracy, too.
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  #5  
Old 07-23-2006, 11:05 PM
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Join Date: Feb 2006
Location: Nottingham, UK
Posts: 261
Re: shoulder bumping

I am using a redding competition bush neck die,So i have used my shoulder bumper die to do the job.
I have set them back 2" so i will get back out there and see if she has worked.
Do the SMKs work well at close range as well as longish range,(About 600y)On small to medium size deer.???
Thanks for the help Bart
Thanks
Colin
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