Chamber questions??

[NorCalMikie]

Got a 6BR with a .272" no turn neck chamber.,I do not turn necks!)
Thinking of another 6BR barrel/project.
All my loaded ammo measures out at .2685" to .269".
The question is: Would there be any advantage to a tighter neck? Maybe a .270" neck/chamber over the .272"? How much clearence is advisable? What are you folks using and why? Any and all opinions are appreciated. Thanks. Mike.

 

[Forum Boss]

Mike,

Jason recently mic'd the neck on his brass for his .272 no-turn chamber. He measured at 4 different spots along the neck, and variance was under 1/2 thousandth. Many people can't beat that unless they are very skilled at neck-turning.

That said, based on what I see in the 6PPC world I do think that thinner necks may have some advantage in maintaining the same neck tension over 10+ reloadings. My theory is the thinner brass doesn't work-harden as fast.

You can build a .268 chamber and do a light clean-up. Terry Brady has a .267" neck, turns brass a little bit and you can't argue with his results.

 

[NorCalMikie]

Paul: Thanks for your input. My question is more toward a "tighter" neck on the unturned brass. Any advantage on tightening the chamber/neck that you know of or heard of?
This is directed more for a "shooter" rather than a "comp" rifle.
I know that there a lot of combinations that make for some fine accuracy. Just working on one angle at a time. Thanks. Mike.

 

[Forum Boss]

Mike,

I wouldn't go less than .0015 clearance over a loaded round for a gun that does field duty. One of our gun of the week authors shoots Lapua loaded ammo and he noted feeding problems in his tight-clearance barrel when the ambient temp was below about 30deg F. The chamber metal shrinks up a bit when it gets cold. Remember, .0015" clearance is only .00075 per side.

 

[BoydAllen]

I would set it up for .002 over a loaded round. One world record holder that I know turns his necks,for a PPC)for "Between .002, and .003." While I know some fine shooters that opt for a lot tighter clearance, evidently something on the order of .0025 is workable.

 

[NorCalMikie]

Thanks Paul and Boyd: Thats the kind of information I was looking for. What the folks are doing in the "real world" makes a difference rather than what we can come up with on paper.

 

[NorCalMikie]

Lynn: Thanks for the input and the offer. Right now I'am in the "thinking" stage of a build.,just planning ahead)
Sacramento might be on the list of places to try in the future but right now I just have to find time to get to the range!,period) Too much to do and not enough time! But it doesn't keep me from thinking! Thanks again. Mike.