neck length vs throat contact

[sigmatero]

<I posted over in Centerfire but they said this would be a better forum>

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!

 

[Rewinder]

Neck Lenght

Ever thought of moving the shoulders back on the case a little. This might decrease case capacity but ,hey, were talking sub-sonic right. There is a 6br short cartridge called the Talldog or something like that. They decrease the case lenght at the shoulders by a tenth to match the internal capacity of 6PPC. Randy

 

[sigmatero]

Thanks for the advice. I actually thought of that but wasn't quite sure how to go about it (I'm a pretty novice reloader- just have been doing standard stuff like .270 and .40 so far).