Is my 6BRA chamber too large?

[WillFS]

I’m looking for advice on a new 6BRA barrel that I believe was chambered a little large. I observed the following using Manson headspace gauges.

On the Go check, the bolt closes easily with a 6BRA Go gauge inserted. When I add 0.004” of Scotch tape to this gauge, the bolt still closes but with light resistance.

On the No Go check, the bolt closes easily with a 6BR Go gauge inserted. When I add 0.002” of Scotch tape to this gauge, this corrects the fit and the bolt does not close.

My assessment is that there is excess headspace of .001 - .002

Is this assessment correct? What would be the consequences of firing from this chamber?

Any advice or comments would be much appreciated. Thanks.

Bill

 

[Poor Shot 65]

Chamber is over sized by ~.002 - it’s a 6bra just shoot it. The brass will be sized to your chamber.

 

[G Liles]

You have to fireform anyway, so what does it matter, just name it something different.
6Bra littlelong!!

 

[steve210]

As long as you size your brass too fit your chamber you'll never know the difference

 

[Ackman]

You don't shoot gauges, don't mess with them. Use a case. Chamber an unfired case. you want to feel some resistance when closing the bolt. That's optimum. If it's just barely, that's fine. If it's more than just barely that's fine too, but better to not have to muscle it down. Try a few cases, new cases can vary, you'd be surprised.

 

[358WCF]

BRA=BR Ackley Imp?

Per P.O. himself, on page 155 Vol. 1 of his 2 book set, for a proper "improved" chamber, the parent cartridge go gauge is used as the no-go gauge & a new .004" shorter gauge will be the go gauge. The brass should chamber with a little "feel" as the neck/shoulder junction will be a slight interference fit.

Stolen from somewhere on the innernet, here's another 1000 words...



Most brass makers dont seem to be too concerned with new brass base to datum measurements anymore. Shorter, as long as it fits in everybody's chamber, is OK & brass life be damned. Personally, I'd rather see empty brass for reloading be a tad long base to datum. That's what sizing dies are for.

 

[swd]

After fire forming back the sizing off for .002" shoulder bump and go shoot...

 

[shoot4fun]

You have to fireform anyway, so what does it matter, just name it something different.
6Bra littlelong!!

how about calling it a 6BRAD(cup)?

 

[WillFS]

You don't shoot gauges, don't mess with them. Use a case. Chamber an unfired case. you want to feel some resistance when closing the bolt. That's optimum. If it's just barely, that's fine. If it's more than just barely that's fine too, but better to not have to muscle it down. Try a few cases, new cases can vary, you'd be surprised.

With my first 6BRA barrel, I found virgin Lapua cases to be mixed in how they fit. Some with no feel and others that needed to be bumped to prevent hard closure. With this new barrel so far, they all fit with no feel.

 

[Ackman]

With my first 6BRA barrel, I found virgin Lapua cases to be mixed in how they fit. Some with no feel and others that needed to be bumped to prevent hard closure. With this new barrel so far, they all fit with no feel.

Years ago I did a bunch of measuring, several different headstamps including Lapua. This was to get more information on AI "crush". Every headstamp, including Lapua, varied is base to neck/shoulder dimension by up to .003 or .004. And difference shortest of one headstamp to longest of longest was .007. Now considering case to case variation, the proscribed .004" 'crush" on chambering for an AI case just isn't realistic. My AI chambers are set with .010' or so crush for fireforming.

 

[Ackman]

With my first 6BRA barrel, I found virgin Lapua cases to be mixed in how they fit. Some with no feel and others that needed to be bumped to prevent hard closure. With this new barrel so far, they all fit with no feel.

With your new barrel, seat bullet with a hard jam.

 

[jackieschmidt]

besides doing my own barrels, I also do my friend Ed’s barrels for our 30BR’s.

For some reason, when I did his first barrel, his headspace came out around .006 different than mine. I still just keep making them like that.

The Rifles shoot identical with our bullet, same load, same everything. His case just comes out .006 shorter.

 

[urbanrifleman]

For years I set my 6bra to zero on a 6br gauge. So that would be 6bra plus two thou.

Personally, I think 4 thou short from 6br is too short for out of the box Lapua to chamber correctly. But that is the "gauge spec" that I do on shouldered Prefits. Since that's the spec.

Best way to set a 6bra nut barrel is with the 6br brass out of the box. It should just drag the bolt on closure.

 

[DaveTooley]

It's best to use caliber/case specific HS gauges. As neck diameter changes the neck touches the non conforming gauge in a different location. Ask me how I know this violates Rule #1, don't do anything to make the phone ring. Consider the case in the picture as a gauge. To many variables involved. Fireform and adjust the sizing die to fit the chamber.

 

[urbanrifleman]

The beauty of the nut barrel really shines when it comes to the Ackleys. You can set the headspace right where you want it. Adjust the barrel not the dies.