neck turn or gauge

[Dave]

I am a 300m shooter using a 6mm BR. I use Lapua brass in a standard,about .270) chamber without neck-turning. However recent checking shows that there is up to .001 runout on my loaded rounds. I am having a new barrel installed and have purchased 200 new cases. Should I clean up the necks or buy a neck wall gauge and just cull the bad cases?

 

[dreever]

Dave,

I've re-read your post and first let me say there is no such word as "about" when talking about a chamber it is a .270 or it isn't, so find out EXACTLY what you have before proceeding further.

So, if you are running a .270 neck chamber without neck turning that's pretty tight especially considering my current lot of Lapua 6BR brass when measuring a loaded round measures .26920. I'd really check those figures since your old batch of brass may not be the same as the new stuff.
A .272 chamber would be safe, perhaps even a .271 if your VERY careful, but a .270 without turning could be dangerous.

Having said all this I'd consider these options:

#1 Keep the .270 neck chamber and do a light turn on the necks to give you at least a .2685 loaded round, .2680 would be safe.
Check EVERY loaded round the first time to make sure you turned enough off the necks.

#2 If you don't want to turn have your smith open up that neck to a .272 Then you can shoot Lapua right out of the box.

I see these two options as the only answer to your question.

 

[Dave]

Thanks for that. I said "about" .270 because my smith said he was cutting a standard chamber, but didn't tell me exactly what it was. However the neck is tight and I am guessing it is smaller than .272. I don't neck turn anymore as the Lapua brass is so good, however it is not perfect. I will take you advice and give a light turn.