6BR neck tension

[Eric Leonard]

with once fired Lapua 6BR brass loaded with 105 VLDH bullets the OD of the necks measure .2685 and with a .268 bushing I can pull the bullets out by hand,,with the .267 bushing seating pressure seems very light but I cant pull the bullets out by hand,,
what effect does going tighter have on things??
do you just test loads with different bushings to see what shoots best or is there something specific to look for in your groups to hint you that you have to little tension,,

 

[mikecr]

What you're seeing is normal given normal spring back(outward) from downsizing.
Tension is not interference fit, it's bullet grip, which is a matter of spring back against .xxx area of bullet bearing.
Tuning tension is adjusting the spring back itself(annealing) and/or adjusting area your spring back grips(sizing length).

I would not bother 'tuning' with tension until I've taken it to stable and intended to begin. If I intended to anneal every time, I would do this during load development. That is, I would not take a good load & hose it all up with a big change to that spring back the load was worked up at.
If results of load development sucked with obsessive annealing, I would stop annealing to adjust tension upward & re-develop. Worth a shot.
Normally I just tweak neck sizing length to adjust tension, and only after full seating and powder testing.

 

[Thumper]

I have a 6 BR with a .271 chamber neck diameter, this rifle likes the tension of brand new Lapua brass with 105 Hybrids. I use a .266 bushing and it works fine but it is less tension than the brand new Lapua brass. I bought a .265 bushing to test but I have not had time yet. I shoot the brass 4 to 5 times until it needs annealed and I sell it and start again with new. The only brass prep I do is sort for weight. I say experiment with different bushing sizes and see how it affects your groups.

 

[Ghansen]

With some shaved necks using a .267 bushing I found the same thing . Initially the necks were cleaned up by .001 and some totally clean at .0015 to see if it made a difference. My most consistent results at distance are with unturned necks, and works with a .267 or .266 size bushing, but a .265 bushing for anything I have turned down. This is with Lapua blue box brass. The effect of neck sizing in terms of accuracy is subjective to all other factors as well, but with a vacuum fit I could still broadly hit the target at 500meters but I could not guarantee seating depth or any form of concentricity with such a loose fit. Still experimenting a little bit now with different bullets until the Berger's come back in. P.S I don't anneal.

 

[Eric Leonard]

between the PPC BRDX and BR I have bushings from 263 to 268,,I trust my 6BR load of 29.6 H4895 CCI450 primers and the 105 VLDH very much,,think I will load 10 each with 267 266 and 265 bushings and see how it goes,

I skimmed the necks on my BRDX brass and use a .265 in its load,,gonna try and not do anything to this new BR brass,,

neck is 272,,loaded round is 2685,,fired case comes out 271 and sized with 267 bushing od is 2674,,

with the 2685 loaded round would a 270 neck be better??

 

[dkhunt14]

In some chambering's, going tighter has improved groups. I think it depends on barrel, throat and where the bullet is seated. I am a in the lands guy and like tension. I don't want them moving when shutting the bolt or staying in the barrel when opening the bolt. Matt

 

[Mozella]

..... snip...........what effect does going tighter have on things??
do you just test loads with different bushings to see what shoots best ....... snip........

Here's my take on finding the best recipe.

In the beginning of load development, I think it's important to weigh powder to the nearest .02gr or .04gr. I prep and sort cases and bullets to whatever level I think I need for my very best competition loads and I seat bullets as accurately as I can. In other words, I try to isolate my experiments to one variable and I believe that controlling all the others in a consistent way is more important than having them all set to optimum, at least in the beginning.

I use a neck sizing die which will at least hold the bullet firmly. Once I settle on a charge weight, I experiment with seating depth. Once I find the best seating depth, then I try to confirm my recipe so that I can have confidence that it's good enough for local F Class competition, which admittedly doesn't require ultra precision performance.

Only after that would I consider experimenting with neck tension. I think neck tension, as it relates to bullet grip, is important, but I suspect consistency is the most important part of neck tension. That's why I anneal each time and pay close attention to my neck dies and case neck thickness. Some folks would call it "good to go" at this point.

Others continue fiddling around to find a slight improvement related to neck tension, remembering that seating depth has something to do with "bullet grip" and how the bullet is released when the powder burns. I suspect there's something to be gained in this area, but I have convinced myself that any improvements are likely to be slight.

Retesting and reconfirming seating depths over a narrow range and tweaking charge weights over a narrow range are likely to produce more improvement than changing neck tension by half a thousandths.............. I think. Personally I'm not going down that road until I improve my wind-reading skills from horrible to simply bad.

When people say they're buying special arrays of 10 different neck dies honed to the nearest .0005" yet they anneal only every 4 or 5 times, I smile.

 

[dkhunt14]

Mozellla, I think Big is wanting to shoot 600 yard BR. In that game you need way more accuracy then F-Class. Some cartridges don't need annealing every time. I anneal my WSM every time and it has showed big improvement by annealing. The Dasher on the other hand has not shown much improvement to any degree. It might have to do with not moving the brass as much on a Dasher or the fact that the neck walls are so thin. Matt

 

[davidpatton]

im still kinda new but over the last few months i have dealt with this a lot. I have a 272 neck and was using a 268 bushing. after a couple firings i could seat the bullets basically by hand. Everyone told me that was way to little tension, but the gun was shooting good. I was shooting at piedmont 600 yard match last year and shot back to back targets with sub one inch four shot group and a single flier about an inch lower. As the more experienced shooters looked at my targets they suggested tightening up the necks one size smaller to hold more consistent. I bought a K&m press with the seating force gauge and started seating with a wilson die. The necks tightened up a bit but it didnt seem to hurt anything, just made more consistent seating pressure which i feel has helped a good bit. I really like the seating force gauge because if one seems to be tighter or too loose you can set it aside and use it for sighters. like i said, im no pro just sharing what i found with my br.

 

[LCazador]

with once fired Lapua 6BR brass loaded with 105 VLDH bullets the OD of the necks measure .2685 and with a .268 bushing I can pull the bullets out by hand,,with the .267 bushing seating pressure seems very light but I cant pull the bullets out by hand,,
what effect does going tighter have on things??
do you just test loads with different bushings to see what shoots best or is there something specific to look for in your groups to hint you that you have to little tension,,

Light neck tension will result in bullets moving from their original seating depth, especially if they're seated into the lands. So a test here is to seat some dummies and then work them through the action and recheck the seating depths. If they do not change and you're confident with the bullet grip, then go on with your load work. IMHO only after completing load work should you experiment with neck tension.

 

[dkhunt14]

Here I actually found a bushing test I kept. As you can see, sometimes the difference can be drastic. I run these round robin, so spreading the condition out and look for best vertical. One thing I will say after being there and doing that. Don't chase a certain seating force, find the bushing it likes and keep it there.

Tom

Tom, my tests showed the same thing. The more tension almost always won out at 1000. Matt