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Controlling Neck Tension

500Stroker

I want to start controlling the neck tension on a no-turn 6BRX for 600 yard benchrest
What is the best or the only method to apply?
I just took delivery of a K&M arbor press with an indicator and I have a custom cut Wilson seater
and a Whidden full length bushing sizer.
Thanks in advance
 
Jim,

I anneal every other time. I can vary my bushing setup by 0.0005 inch, but haven't had any reason to go any tighter than the 0.2630 bushing I'm using. With a no-turn neck, I'd skim the necks so about 50% is turned. I'd also go with whatever bushing gives you about 1.5 to 2.5 thousandths clearance. With the K&M I sold you it is set up to measure very light seating forces. You might need to go with a 0.001 indicator if you have heavier neck tension.

When you say "no turn" is that a .2704 neck or the .272? I had an 8-twist 6BR with a .2704 neck and my measured cases were .268 with "skimmed" necks, giving me .002 clearance. The thing would shoot Berger 80 grain FB lights out.

Dennis
 
500Stroker said:
I want to start controlling the neck tension on a no-turn 6BRX for 600 yard benchrest
What is the best or the only method to apply?
I just took delivery of a K&M arbor press with an indicator and I have a custom cut Wilson seater
and a Whidden full length bushing sizer.
Thanks in advance
Click to expand...
Normally you would adjust tension(bullet grip) with normal sizing LENGTH, which you can adjust with installed Redding or Wilson bushings in your die. 'Normal' sizing here being ~1thou under cal after spring back & expansion & spring back against seated bullet bearing(no further), and assuming your bullet bearing is not into donut.
In order for your seating force to correlate with tension adjustments, your seating friction must satisfy a very consistent standard.
Best money can buy here is already provided with the carbon layer left in the necks (with firing).
But you need to understand, seating friction is not neck tension, as shown by annealing.
 
DeltaBravo said:
Jim,

I anneal every other time. I can vary my bushing setup by 0.0005 inch, but haven't had any reason to go any tighter than the 0.2630 bushing I'm using. With a no-turn neck, I'd skim the necks so about 50% is turned. I'd also go with whatever bushing gives you about 1.5 to 2.5 thousandths clearance. With the K&M I sold you it is set up to measure very light seating forces. You might need to go with a 0.001 indicator if you have heavier neck tension.

When you say "no turn" is that a .2704 neck or the .272? I had an 8-twist 6BR with a .2704 neck and my measured cases were .268 with "skimmed" necks, giving me .002 clearance. The thing would shoot Berger 80 grain FB lights out.

Dennis
Click to expand...
Not sure of the neck dimension, i'll find out and report back on that.
The is new blue box Lapua brass
After I size it with my Whidden full length die with a .266 bushing the inside of the neck is .239, this appears very tight, the needle on the press looks like a airplane prop on take off. Plus I think it my be causing some pretty high pressures, as it punched out some primers with only 33.5 gr of Varget
 
I think you need to get a .267 or .268 bushing; that .239 inside neck measurement gives you about 3.5 thou neck tension and that could be causing some pressure issues. I also recommend going very slowly when seating the bullet to get a feel for the process; if that doesn't work out, get a 0.001 dial indicator for the heavier seating force.

After I've sized the case, I use a Q-tip to wipe out any lube inside the neck and then run a drill-mounted brass brush into it to smooth it out and even up the carbon.

For my previous comment, I forgot to mention that I now use a .266 necked 6BR, making the .263 bushing a little more understandable.

Dennis
 
First, I would turn the necks very lightly to get them more consistent case to case.

Second, if you have not already, get a nylon bore brush and use it to "clean" the inside of the necks before loading. IT is amazing to me the difference in seating force required with and without this step.

Third, be sure the cases have the same number of firings since either new or having been annealed. If you are annealing, run the case back through the neck sizing stage and brush the necks again.

You are on the right path.
 
DeltaBravo said:
Jim,

I anneal every other time. I can vary my bushing setup by 0.0005 inch, but haven't had any reason to go any tighter than the 0.2630 bushing I'm using. With a no-turn neck, I'd skim the necks so about 50% is turned. I'd also go with whatever bushing gives you about 1.5 to 2.5 thousandths clearance. With the K&M I sold you it is set up to measure very light seating forces. You might need to go with a 0.001 indicator if you have heavier neck tension.

When you say "no turn" is that a .2704 neck or the .272? I had an 8-twist 6BR with a .2704 neck and my measured cases were .268 with "skimmed" necks, giving me .002 clearance. The thing would shoot Berger 80 grain FB lights out.

Dennis
Click to expand...
According to my GunSmith the neck is .2705
 
500Stroker said:
According to my GunSmith the neck is .2705
Click to expand...

Back when 600 yds bencherst started. A group of us were shooting 6BRX NO-Turn necks, not turning necks and setting records. The 6BRX I shot 3 IBS 600yds records with, was a 0.271" neck, I run a 0.267 bushing. Don't fool with turning neck. I was 0.015" into the lands. I wanted enough grip for the bullet not to move. Start with a 0.267" and be sure you have a good chamfer on you necks with a VLD reamer. 33.5 gr is a stiff load of Varget, may be your primer problem. Get your speed at 2975 f/s, that is the best speed for the 105 and 108 Berger. any faster is not needed. The 6BRX can run 3100 + but I have had 5 - 6BRX barrels, they all shoot at 2975 f/s.

Mark Schronce
 
MarkS said:
Back when 600 yds bencherst started. A group of us were shooting 6BRX NO-Turn necks, not turning necks and setting records. The 6BRX I shot 3 IBS 600yds records with, was a 0.271" neck, I run a 0.267 bushing. Don't fool with turning neck. I was 0.015" into the lands. I wanted enough grip for the bullet not to move. Start with a 0.267" and be sure you have a good chamfer on you necks with a VLD reamer. 33.5 gr is a stiff load of Varget, may be your primer problem. Get your speed at 2975 f/s, that is the best speed for the 105 and 108 Berger. any faster is not needed. The 6BRX can run 3100 + but I have had 5 - 6BRX barrels, they all shoot at 2975 f/s.

Mark Schronce
Click to expand...
The neck wall thickness on my brass is 0.0125.
Does that work for a 0.267 bushing? Or should I try a 0.268?
Thanks for the speed info,very good.
 
500Stroker said:
Not sure of the neck dimension, i'll find out and report back on that.
The is new blue box Lapua brass
After I size it with my Whidden full length die with a .266 bushing the inside of the neck is .239, this appears very tight, the needle on the press looks like a airplane prop on take off. Plus I think it my be causing some pretty high pressures, as it punched out some primers with only 33.5 gr of Varget
Click to expand...

That seems like a pretty hot load. You might want to try some varget loads in 32.0-32.5gn range.
 
dkhunt14 said:
.265 or .266 Matt
Click to expand...
I tried a .266 bushing
After I ran the brass thru the die I would end up with a .239 inside neck dia. ?
Using .243 bullet that leaves me with a -.004 neck to bullet interference fit, way to tight.
I ordered both .268 and .267 bushings to try.
 
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