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Concentricity?

 
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  #1  
Old 04-02-2011, 10:29 PM
kc kc is offline
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Concentricity?

What should I do to a case when measured after pressing cleaning and triming and is out of round .003 of an inch? and the bullet wables.
Should I toss this case?
Shoud I order a neck sizing die?
I use a digital calper on all my cases
and after the load is done, I cycle every round to make sure the finished round is not to long.
I find bluing die is a big help, I make sure all my finished rounds are just touching the lands.
this way I know if I cycle one the round, it will not latch on and pull the bullet out of the case.
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Old 04-03-2011, 02:50 PM
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Re: Concentricity?

To know what we are doing about runout we must have a concentricity gage. Sinclair's with the lower cost dial indicator is perhaps the best value available today. I use my gage to find where runout is coming from and fix it. I have no use for any such tools as Hornady's expensive 'bend 'em straight' device.

Concentric cases are a prerequisite for concentic reloads and the cases are the most difficult problem. Conventional neck dies do nothing for concentricity that a FL die will not do. Obtaining concentric cases (necks actually) frequently requires neck turning to uniform the common manufactoring inconsistances. The "best' neck turners are hand held tools and the best of them are quite costly but loosely fitted factory chamber rifles don't even benefit from such precision. I believe the Forster (HOT-100) hand turner is the best value on the market for factory chambers, about $50 from MidwayUSA last time I looked. Use one to skim turn most necks about 60-80% and that's as thin as we can benefit from. Then we need a sizer-expander combo that won't 'bend' our nicely uniformed necks. For factory rifles I prefer the Lee Collet neck sizer for straight necks; for "FL" sizing I use a 'body die' and follow that with the Collet sizer.

Seating at/in the lands is a BR technique for their tightly fitted chambers and not all BR shooters do it. Few factory rifles shooting with common cases and bullets do their best seated against the lands. I suggest starting from 20 to 30 thou off the lands until finding the best charge weight, then vary the seating depth in and out in maybe 5 thou steps while using that charge until you find the BEST OAL.

IF your conventional seater die has tolerances that work together it will seat as precisely as any other but that's not common. Most conventional seater dies are moderately precise and there is no real advantage to any given brand that I've been able to measure. But, Forster's BR and Redding's Competition seaters ARE consistantly very good. NONE of the other threaded type so-called "comp" dies, at any price, give any better concentricity on average than less costly conventional seaters. IMHO.

No matter what we do, some cases will persist in run-out problems. Any that continue to show significant run-out after all my processes get tossed.

Last edited by boomtube; 04-03-2011 at 03:10 PM.
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Old 04-03-2011, 03:30 PM
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Re: Concentricity?

Three thousandths runout is not much to be of any concern. Ammo with that amount will easily shoot 1/4 to 1/3 MOA at 100 yards and 1/2 MOA at 600 yards. Example; commercial .308 Win. match ammo in properly accurized M1 and M14 rifles with mil spec chambers and bullets not touching the lands. Even 7.62 NATO match ammo with a good lot of primers with 4 thousandths runout would shoot 1/2 MOA at 100 yards, 3/4 MOA at 600.

Note that with most cartridges, the front of the case is centered in the chamber by the matching angles of case and chamber shoulder. That well centers the front of the round in the chamber, especially when the firing pin pushes the case a few thousandths forward until its shoulder stops against the chamber shoulder.

Best die for resizing fired bottleneck cases are full length busing dies that don't use expander balls. They typically make the straightest case necks. And the accuracy they enable is seldom equalled by neck only sizing dies. Just be sure the bushing diameter's only 2 to 3 thousandths smaller than a loaded round's neck diameter. Sierra Bullets uses these dies on most cases that fire their bullets for accuracy testing. They use standard full length dies for the others.

If the case neck's not straight, I've not found any seating die that'll seat bullets straight. Why? The case neck usually bends a bit when the bullet's seated, but springs back afterwords. I've tried Wilson, Bonanza, RCBS, Vickerman and several other so-called straight line bullet seaters; not one made a case neck straighter after seating bullets. Redding's web site has a good article on this.

Last edited by Bart B; 04-03-2011 at 03:35 PM.
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Old 04-03-2011, 03:57 PM
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Re: Concentricity?

don't take a lot of the advice you get as "gospel", use what works for you. I neck size for 300rum/243ai/and one 223, most others are fl sized. I load two rifles to the lands, others where it works best, and happen to have great luck with rcbs comp. seater dies. try several methods/dies till you find your particular "sweet spot" and run with it.
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Old 04-03-2011, 09:55 PM
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Re: Concentricity?

"....happen to have great luck with rcbs comp. seater dies."

Ah, yes. But the question is, do they make any better ammo than an average set of conventional dies? After all, most conventional dies are quite good.
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Old 04-04-2011, 07:24 AM
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Re: Concentricity?

Quote:
Originally Posted by boomtube View Post
"....happen to have great luck with rcbs comp. seater dies."

Ah, yes. But the question is, do they make any better ammo than an average set of conventional dies? After all, most conventional dies are quite good.
ah. yes, but the answer is, yes they do. conventional dies are ok for the most part, but rather crude in seating stem adjustment, "twist and guess", and seldom repeatable round to round.
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Old 04-04-2011, 07:47 AM
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Re: Concentricity?

Use the concentricity guage as a tool for troubleshooting. If you are happy with the groups you are getting then dont bother...
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