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Neck Clearance

 
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  #1  
Old 12-09-2002, 08:03 PM
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Join Date: Dec 2002
Location: Northwest MN
Posts: 76
Neck Clearance

Hello to all!

Hopefully a few of you might offer me some insight; I could certainly use it. What I would like to know are some numbers on neck clearance that some of you utilize. Currently I'm running a .338-378 with about .0015" clearance *per side*, and am thinking when the throat goes to hell <the eneviditable, sadly> I may try something tighter. In the meantime, and more pressing to me, is another project {it's a mouse-gun, but no laughing now!}, based on a 6PPC with a sharp shoulder <40 degree>, firing 95gr VLDS. I am thinking a half-a-thou per side. So what do you fellows run? I admit, I like things on the tight side [don't post my comments on FriendFinder, please [img]images/icons/shocked.gif[/img] ], but would truly appreciate a few experienced comments. pros, cons, etc. Primarily, this will be a bench number, and I'm a meticulous cleaner, so blowing my digits off shouldn't occur.... [img]images/icons/grin.gif[/img] Thanks, guys. One of these days I'll get smarter and can help inform some of the goofs like myself!

Dave
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  #2  
Old 12-09-2002, 11:37 PM
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Join Date: Jun 2002
Location: middle Tennessee
Posts: 379
Re: Neck Clearance

Bruce Baer runs .0015" clearance per side in his 1000 yard guns, so your clearance in your super thumper is spot-on. But wait, you asked what we are running. I have both a 6mm PPC with the standard .262 neck and a 6mm Remington Ackley Improved with a .266 neck. I run .0010" per side in each and it seems to work very well in my rifles. I also run .003" tighter bushings(.257 and .261 respectively) in my Wilson hand dies. You can have my $0.02. [img]images/icons/wink.gif[/img]
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Old 12-10-2002, 02:45 AM
daveosok
 
Posts: n/a
Re: Neck Clearance

Is their any correlation between case capacity and velocity when setting up for proper neck clearance?
What determines how much you need and is their a standard to use when figuring out the proper clearance?
As I understand it, neck turning allows consistant releasing of the bullet when fired, thus a few things happen as I'm thinking here.
One with consistant release pressure I think that youll see less extreme spreads of velocity?
Two if the powder performs consistant youll end up with consistant barrel harmonics?

Any merit to my thinking?
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Old 12-10-2002, 03:03 AM
 
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Re: Neck Clearance



[ 07-12-2003: Message edited by: S1 ]
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  #5  
Old 12-10-2002, 05:43 AM
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Join Date: May 2001
Posts: 5,949
Re: Neck Clearance

S1

You seem to be a measuring kind of a guy and I like that. In your opinion, at 1,000 yards, how much is group size affected by not neck-turning? How much would an otherwise (let's say) 10 inch group be improved by turning?
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  #6  
Old 12-10-2002, 08:10 AM
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Join Date: Jun 2007
Location: Wilmington NC
Posts: 4,222
Re: Neck Clearance

Cybra,

On the 6mm BR, I am building a 6mm BRH now (shoulder moved forward .200 and 45 degree shoulder and .265 neck). This design is similar to the popular 6mm BS (Baby Shehane). It will be used with 95-105 VLDs from JLK in a 28" HV taper Spencer barrel with 1-8 twist. My plan is to be .0005-.0007 per side with Lapua brass. Good 600 yd BR gun, egg shoot and backup LG.

Dave Kiff made the reamer. My 1000 yd guns I set up to have .001 or less on each side. Intersting side note on clearance. Some of the early top dog LR BR shooters shot magnums with .003 clearance on each side as they thought that was best way to shoot magnums and consistently won. Now the same guys are using standard BR clearances of .001 and group sizes has shrunk by 50% on average at least. 2-3 years ago, you could win IBS LG with a 6" group consistently, now it takes 3-4". HG would win with 9-10" now you must shoot 4-6"

Personal opinion is that tight neck turned cases are more uniform, give more uniform release, MV, SD, ES etc. The LR BR shooters have found that we can control the tolerances as tight as the shortrange BR shooters with good tools, loading techniques and cleaning. Look at the results at the last nationals on group sizes for both LG and HG. Quality tools and procedures such as K & M neck turner are key. I have tried all of them and his is the absolute best (in my opinion). You can turn to .00002 precisely. His tools are a top choice for BR shooters.

Good luck

BH
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  #7  
Old 12-10-2002, 11:27 AM
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Join Date: Jul 2001
Posts: 1,459
Re: Neck Clearance

Cybra, I too shoot a 6BR with a tight neck and it is one of my best shooters. One thing to consider, are these rifles going to be hunting? If so, are you going anywhere where rain/humidity or dirt could be an issue?

Although we have done everything to make our rifle chambers and ammo clean, a little bit of moisture on the necks/chamber due to rain or condensation while out in the field could now cause clearances to go to zero. Water does not compress very well.

I like tight necks for my BR and varminting rifles where I can control everything but get a little nervous if used in a "working" rifle.

In Canada, some of the best places and times to hunt get you in pretty wet, cold/snowy or mucky conditions. I neck size my brass and use normal SAAMI neck dimensions. Accuracy is around 1/2 MOA which seems adequate for any of the big game hunting I am likely to do.

Something to think about...

Jerry
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