neck tension on bigger cases/slower powder

C

chris 308

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My 6br seems to shoot well with .001 neck tension and a bullet jammed .020 with vv n140 powder. With .003 tension I can see the groups open up with lots of verticle. This is at 1k
My 300wsm has a loaded o.d. of .336 give or take .0001 with a berger 210 vld. What is a good neck tension for this. I have tried a .332 bushing but do get 8 or 9 shots tight and 1 or 2 out. I was told that the slower powder/bigger cases like more squeeze to allow the slow powder to build up pressure. What do you folks think? Woukld going to a .333 or a .334 bushing (.003 or .002 neck tension) change for better or worse?
 
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i would have thought in theory that to be true also. but my 338 lapua imp seems to like minimal tension with retumbo. i havent got around to testing apples to apples yet, as it is still b.r. season and this is just a fun/long range hunting gun. i can tell you my best group to date @300 came while trying to find pressure limits. i found it at 102ish grains so i had to pull 5 apart and dump some powder. i placed the bullet back in with my fingers and seated them with the bolt, it then shot them into a 5/8" group at 300. the neck area was a bit blackened but no more so than with 3thou squeeze. so??? a person just needs to try it all and see what works best in the end.
 
I'm tying a .334 bushing (.002 neck tension) this weekend at a 1k shoot compared to .003-.004 that i've used in the past.we'll see how it goes.This is with a 300wsm/n 165 powder. I do know that my 6br shot much better after i switched to only .001 neck tension, but that was with a much faster powder.....chris
 
Chris

I'm using 0.002 in my 7WSM using the Berger 180s and 66+ grains of H1000 (before that I used RL-25). 2 thou seems to work well, but I have not tried it with less tension, even though I jam the 180s 0.10-0.012.

JeffVN
 
chris,

i struggled with a 7wsm for a while and tried from 4 to 1 tension jammed hard to jumped a ton. 2 seemed best there also, and the one thing i noticed was crappy runout with 3-4 tension. almost every one had to be bent on. of course i gave up and use my 17# dasher in both classes, but if i had to pick one it wouldve been 2 thou, with around 12 jump on the 180 berger.
 
.336 loaded round sounds like a really thick neck.

Turn the necks some and work with the tension there. I don't think you will find many competitive WSM shooters with necks that thick answering here.

I'd guess that most 30 cal shooters use a loaded round size of .328 to .332 (most meaning 90%). I use .329 as my favorite number and I have big necks in my guns. That's not to say some might not be larger but neck tension is a bit tough to get a good handle on when the necks get too thick. In my opinion, .336 is a little bit too much neck wall. Now, probably when I say this someone will shoot 10 shots in 2 flat with a .339 loaded round.

Nothing is for sure in shooting.
 
In my .308 I use a .336 bushing for unturned Lapua Brass, so .334 is in the realm of possibility, especially if you are using Winchester brass, which in my experience had thinner necks.


JeffVN
 
I have a 300 wby with a 330 nk. Loaded rounds are measuring .328. I am using a .322 bushing, down from a .324 and .326. I seem to have taken care of most of the vertical at 1 K, and have single digit ES. I am going to tinker with non magnum primers next.
 
I talked with Bill Shehane and He suggested using a lot of neck tension(.003-.004) As it turned out we uncovered another problem. i have a .337 neck and a .336 loaded round is a bit too tight. might explain the flyers(??). I took my loaded o.d. to .335 and will try .003 neck tension(.332 bushing) and see what happens. i guess "br type cases" are just the oppossite of the big boomers as far as neck clearence and neck tension. thanks folks!! chris
 
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This discussion is something I have been thinking as well. I have noticed that with some of the slower powders, once I get to a certain powder weight, I can keep adding more, but velocity doesnt increase. I am thinking that this is because the bullets starts moving too early and some of the powder turns into a near solid block behind the bullet and doesnt burn? Is this right. I was wondering if going to slightly more neck tension with the bullets jammed into the lands might get the powder to burn more completely before the bullet starts moving.
 
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