.308 Win. New lapua Brass- neck tension interferance fit question

[kawzak]

I have not measured the Lapua brass neck (I.D.) or my 168 SMK bullets (O.D.) yet. What should the interference range be? I have inside/outside mics that can read .0000". I understand consistent tension (light?) is a contributor to accuracy. These will be fed/shot (one at a time) from a Rem SPS 308 bolt rifle.

 

[Shynloco]

kawzak,
Not sure what you are referring to when you use the term, "interference range." I suspect you mean "Neck Tension" or "Neck Clearance". The first refers to the tension of the casing neck that hold the bullet in the casing. The second term I used refers to the "clearance" between the outside of the casing neck and the chamber wall of the barrel. Both are usually in the area or .002 - .003. Now some folks even load their NECK TENSION (that holds the bullet inside the neck of the casing) at .001. I try to keep mine at .002. Hope that helps.

Also remember, that when you talk about a Rem SPS (nice Rifle), it is an "across the counter" rifle which means it has a SAAMI spec chamber and not a custom chamber that is cut with a very specific reamer (neck and neck tension/neck clearance) factored into the set up. That's not to infer that a light neck tension won't help you in your accuracy. But very specific sized chambers are easier to tune your ammo for ultimate accuracy. Info only. Good luck and have fun.

Alex

 

['Freak]

Most folk lacking means to accurately measure case neck ID, or whatever, will figger ‘neck tension’ is the increase in the case neck outside diameter measured before and then after seating the projectile.

 

[KevinThomas]

Kawzak,

For what it's worth, we normally recommend that you run new brass over an expander mandrel before loading for the first time. Normally, you're looking for a size of about .306", which should pass through with a minor amount of resistance. In selecting a bushing size fro subsequent reloadings, I'd use this as the baseline I.D. to shoot for, but your particular loading may be a thou or so in either direction. Just a starting point, but your rifle will tell you what it prefers.

 

[kawzak]

Thanks for the replies- that is the info I am looking for. looks like .001-.002" is the interference dimension between inside of the neck I.D. and bullet O.D.(before loading). I was thinking it would be like .0005" or so (a lot less) I know my rifle is not a custom target rifle. Reguardless I enjoy getting the most out of anything I work with, and I have the measuring equipment to check. My concern is consistency in size/dimensions.

 

[ryanjay11]

Get a .336" bushing if you aren't neck turning.

 

[Sugar]

Interference is another way to describe pinch or tension. I use .002 of neck tension (interference) on my savage and remington factory rifles.