Can't figure out the math!!!!

[rsbhunter]

Ok, i'm new to using neck sizing dies that use bushings. If a chambers neck dia is .298, as in the 6.5x284 Win. and the Norma 6.5x284 is .300...(per another post) why is the new brass neck dia , both lapua 6.5x284 and Rem 260 measuring .291 loaded? Everything i read , and all of the help i have gotten says to neck size .002 under a loaded rnd.s od neck dia.That figures out to sizing the neck around .009-.011 each time......is this the norm? Some have said no, but alot of what i read shows these #s (.298 neck chamber) as the spec....been in this game awhile, and i'm STILL learning new facts every day!!!!! Thanks for any help....rsbhunter

 

[Erik Cortina]

If your loaded round is .291" then you need a .289" bushing, that will size it down .002".

Now, if your gun has a .298" neck diameter, that means that you will be sizing it down .010" every time, but most match chambers have a .294" or so chamber if they are a "no turn", smaller if it is a "neck turn" chamber.

A .298" chamber is probably meant for hunting, which will have plenty room so that even a dirty chamber will be safe. Factory chambers usually have looser tolerances than match chambers.

I hope that answers your question.

 

[Erik Cortina]

Fired cases and bushing size have nothing to do with each other! What if you have a very loose chamber?, then the bushing will not size the brass enough to grip the bullet.

Measure a loaded cartridge and deduct .002" from that measurement and that is the size bushing you will need regardless of chamber size!

 

[Cheechako]

Erik

You're right. I'm wrong. I'm a Benchrest shooter and was thinking in terms of tight necks and fitted cases.

My post is deleted.

Ray

 

[mikecr]

Ok, i'm new to using neck sizing dies that use bushings. If a chambers neck dia is .298, as in the 6.5x284 Win. and the Norma 6.5x284 is .300...(per another post)

You were led astray with any of that...
Your .291 loaded necks are 13.5thou thick which is completely normal. 1-3thou of clearance beyond that (.294) is plenty for ANY use.

If your chamber really is .298 or larger, for 26cal, you can't even use a single bushing for proper sizing. It's FL sizing only for you.

 

[rsbhunter]

Erik, i do understand about what measurements they were saying to use, i stated in the OP that you take a "loaded rnd's od"..and Thanks for all the answers, if i need to full length , then thats ok...this is 97% hunting rifle....no formal bench use...Thanks again for all the help...rsbhunter