throat contact vs neck length

[sigmatero]

I cross-posted over at another site but it seems to be more of an advanced topic so I'll try here, hopefully you all can give me some advice...

I'm pretty new to reloading, especially wildcats, but I've recently read The Ultimate in Rifle Accuracy and have been inspired to load as accurately as I can.

I'm working on a 338BR aka 338 Whisper (7BR necked up to .338 for use in subsonic application with 300 gr Sierra Matchking). I'm currently building up a single rifle shot for accuracy but later want to use the same cartridge in a AR-15. I'm getting a custom chamber cut so have some flexibility there.

The AR has a max COAL of 2.260 to fit in the magazines. Because the 300 gr SMK is so long, when I insert the bullet to the COAL I'm about 0.09 shy of the ogive tangency so essentially the full diameter portion of the bullet is buried in the neck.

The neck of the cartride is about 0.32 long and I have room to recess the bullet deeper (powder capacity shouldn't be a problem since I'm subsonic).

For accuracy, what is more important- more brass neck or more contact with the throat?

From experience, how short of neck can I get away with and still have a cartridge that isn't too delicate (which could cause feeding problems in the AR).

And from experience how much contact with the throat is typically required?

Thanks folks!

 

[sigmatero]

crickets....

Anyone have some advice for me on this project?

Thanks!

 

[blawton]

As long as you have at least 1/2 the caliber in length on the neck you should be fine. It sounds like you just need to shorten the freebore and the neck of the chamber up to get it to fit in the ar mags.

 

[blackbrush]

you just need to shorten the freebore and the neck of the chamber up

Would you please elaborate.

 

[RJinTexas]

I would suggest that you contact Robert Whitley @ 6mmAR.com he specializes in building AR uppers and most likely could steer you in the right direction.

RJ

 

[blackbrush]

he specializes in building AR uppers and most likely could steer you in the right direction. RJ

My question is not AR specific...in fact, I don't know which end you put gas in that horse. My brain is MUCH smaller and thinks MUCH tinyer than a simple bolt action, e.g., Rem 700.

 

[RJinTexas]

blackbush, my suggestion was directed to the original post by "sigmatero" as he stated in HIS POST that he later was planning on chambering the 338 Wisper in a AR.

RJ

 

[blackbrush]

Things become more clear the more I read what I read and didn't understand. Now I understand where the AR reference originated...

Thanks!