Neck diameter for no-turn 6BR?

[Steave]

I presently don't own a 6BR, but am going to either buy one or have one built in the very near future. It will be used as a varmint rifle, not a competition rifle, so I have no interest in turning necks. Since it appears that Lapua has changed the neck thickness on their brass the old standard of .272 for no turn might be a bit on the loose side and .270 might be better.

So what is the consensus of those of you who are 6BR experts, what diameter should I specify, .270, .271 or should I stick with .272?

Thanks for any and all advice!

 

[RonAKA]

Buy all the brass you think you need for the life of the barrel from the same lot first, and load 20 rounds or more. Measure each neck OD twice at 90 degree points, to 0.0001" accuracy. Take the largest dimension you get, and double check it. Then add 0.002" and specify that for your chamber neck.

 

[Klong]

For a varmint gun I would use only Lapua brass and chamber .272 .

 

[Obtunded]

5 thou clearance is SAAMI spec, and if you are using a repeater, the extra clearance can't hurt. I say stick with .272 and that will allow you to use any brass. Mr. Whitley (RCW)on this board seems to spec all his reamers with generous neck clearance and it doesn't affect his accuracy.

 

[oklahomaboy]

Dave Kiff of PTG Reamers is solid in his position that the 272 is his no-turn dimension. I was planning a new 6BR repeater and ordered the new blue box brass and a 272 neck reamer from PTG. I quickly discovered the thinner necks on the new brass. I simply won't chamber a new rifle with a reamer with .004-.005 clearance in the necks. I contend the more you size your necks, the more opportunity you have to increase your runout and work harden the brass. If you order a 270 neck reamer, it will fit new brass but you will have to turn necks of future brass (and older brass). This might effect resale of your rifle later on. I like .002 total clearance over no-turn loaded rounds so I reordered a 6XC reamer and sold the 6BR brass. I will use the rifle for coyote and an occasional deer so the 6XC gives better ballistics and will likely feed better. As a side note, Kiff indicates thicker necks will return with the next batch of Lapua brass. For this reason, he is 100% correct to stay with the 272 dimension for a no turn reamer.

 

[Steave]

Thanks, guys, I appreciate your thoughts and info!

Steave

 

[Phil]

Buy all the brass you think you need for the life of the barrel from the same lot first, and load 20 rounds or more. Measure each neck OD twice at 90 degree points, to 0.0001" accuracy. Take the largest dimension you get, and double check it. Then add 0.002" and specify that for your chamber neck.

Ron,

I like the way you think.........

 

[SS427]

There is a post on Benchrest Central that indicates Pacific Tool and Gauge is changing the dimensions of the no turn BR reamer. The previous no turn reamer measures .2720 and the new "blue box" reamer measures .2704.

Only repeating what I saw there tonight. I would call PTG to verify the situation.

I agree w/ Ron. Buy a complete supply of brass for the barrel and order your reamer based on that supply of brass.

I have a .272 neck and I'm not sure my brass for this barrel will last the duration of the barrel. I have to wonder what Lapua will do in the future. Will they go back to thicker necks is or this a permanent change? If I was to order a reamer today, I would go with a smaller diameter than .272. Even if Lapua goes back to a thicker neck, you have an out by turning the brass slighty.

 

[RonAKA]

See this post by Tommy Leroy Johnson. It suggests Lapua will go back to the thicker cases. It also gives suggested reamer dimensions for the new current brass.

http://www.accurateshooter.com/forum/index.php/topic,3750245.msg35882302.html#msg35882302

 

[deadlyswift]

I too read this post. I would have to think that Dave Kiff does have a good inside source to say that. As RonAKA stated before order enough brass to last you the life of your barrel. Get a Avg. mesurement of the loaded dia of this lot of brass. Then choose your neck dia. .003 or .004 what ever clearance you desire and then decide what your neck dia will be. Some claim that they are getting as much as 30+ loadings with the 6br brass. I don't doubt they are, but I bet they are working the brass at a min. No doubt working the brass at a min is a plus!!!!
Mark

 

[dreever]

Makes me wonder.

I've had a bag of "culled" neck turned 6BR brass a real mismash of neck diameters from setting up neck turners. Real junk or so I thought. I picked a neck bushing that sized some and barely touched others(.267 bushing) loaded them up with my standard 6BR load and headed to the range today. Loaded round diameter for my .269 chamber ran from .26475-.26780 nothing consistant that's for sure. I have been anally sorting my loaded round Match brass to .26725.
Conditions were pretty good with just a hint of some wind and mirage.
Here's how the crap brass shot. All are five shot groups off the bench:

200 meters= .400 inch

300 meters= .460 inch

500 meters= 1.120 inch


Fluke? Maybe,but does warrant some more testing. I'm actually going to shoot this brass in our Match this Saturday.
This sort of shows me that all this worry about necks might not be that big of a deal. If you have a good tight custom chamber and seat into the lands perhaps that difference in neck expansion isn't as critical as one would believe.

Danny