6bra #1 .268 neck

[blundby]

Finally got my barrels chambered. Test feeding dummies I find i need to take the 6br lapua brass down from .013 to .0095 to feed without fiction when closing the bolt. Loaded rounds that feed right measure .2600. Loaded non turned brass measures. 2675. I use a high quality starrett tube micrometer.

Does this mean the JGS reamer I have actually is a .262 neck? Will having such thin necks be a problem? I do not have a smaller bushing than .262. Will fireforming with so little neck tension be a problem?

 

[DngBat7]

If you have the reamer, why don’t you just measure the neck on it with your calipers?

 

[6BRAckley]

Make sure your cases aren’t hitting on the juncture of the neck / shoulder. Slightly bumping the shoulder MIGHT be needed to get the case to chamber with slight resistance. Turning the necks as much as your are could be cutting enough in the shoulder to make the bump not necessary but you are leaving yourself with a neck too thin IMHO.

 

[dogdude]

I cut my #1 .268 to .105, plenty of clearance, .264 loaded.

 

[group therapy]

mine is a .268 and I turn mine to a TINY bit more than .011. your reamer should be measured like someone else said. good luck!!

 

[newbieshooter]

When I first started on the 6BRAI (.268 neck), I had a hard time closing the bolt on my newly turned cases (.0112 at the time - .266 loaded round). Called Alex and learned my chamber is -.004 at the neck shoulder junction - so there's going to be a crush fit when attempting to close the bolt on newly neck turned brass. So hard to close bolt wasn't related to my neck turning or anything to do with not taking enough off the necks. I could bump my cases (as jmp mentioned) a wee bit so there's a slight crush fit which will help make bolt closure on new cases a wee bit easier. I was taught that a slight crush fit (just keep bolt lubed) was a good thing for fireforming new cases...

YMMV

 

[jackieschmidt]

First and foremost, you must find out what the actual neck size is on your reamer. Do not proceed any further until you do that for sure.

You can use a set of dial calipers if You are familiar with them. Hold the reamer vertical, and gently closet the Jawas until you fell a slight contact, being careful to keep the caliper square. Gently twirl the reamer to ascertain the the highest points to the opposite flutes. Do it several times to be sure you get an accurate measurement.

 

[blundby]

Tanks for all the advice. Tried bumping the shoulder back 5 thousands but it had no effect. It is fresh lapua brass. They are in my experience always roomy with regards to headspace. Turning the necks had an effect though... Will measure the reamer when i get home. I shorts prs and am not looking for ultra thin brass necks..

 

[Alex Wheeler]

When you turn the neck you cut into the shoulder a little bit I assume. That shoulder junction is where the virgin case headspaces. So the more you cut into the shoulder the looser the case will be. Try bumping the case with a 6br die, bumping a virgin 6br case with a 6bra die doesnt work well.

 

[blundby]

Figured it out i think. Sized the virgin brass with the bra die and i managed to chamber rounds only with neck walls turned down 2 thousands. Loaded rounds measure .266 which ahould be right. Fireforming loads (105 scenar, 29 gr n150) shot 1/3 inch groups. Extraction was a bit stiff, perhaps I need to be more careful removing sizing wax?