Comments on: Myth Busters II – Bob Crone’s 6mm BRX – by Robert Whitley

By: Tim Claunch

Tim Claunch — Sun, 26 Aug 2012 20:53:38 +0000

My first BRX reamer was a total disaster. I had to trim 6BR brass .015″ before they would chamber in the BRX. I called the maker Dave Kiff, and he told me that was the original Crone design, that he had to get permission to copy the design. I will take a picture of the reamer print for display if anyone wants to see it. After this story I know [the reamer was not correct].

By: Editor

Editor — Tue, 24 Aug 2010 16:05:01 +0000

Boyd,
Here are Roberts comments on the body dimensions of the BRX:

Here’s some info for you on BRX brass (resized and ready to load).

Base to shoulder = 1.170″
Base to neck/shoulder junction = 1.333″
Overall case length (fired 2x and re-sized 2x) = 1.547″
Shoulder diameter (resized) = .459″
Diameter .200″ forward of base (resized) = .470″
Neck diameter loaded = .269″

Some comments:

The BRX reamers I have (both Kiff and JGS), per the prints, are .470″ in diameter at .200″ ahead of the base of the case, but honestly, the chambers with both reamers wind up maybe .001″ – .0015″ larger there for a few reasons:

a. The tolerance on the prints is + .0005″ and after having a variety of reamers measured in a comparator, it seems most reamer makers seem to stay in the plus side of the tolerances (probably for liability reasons); and

b. What I typically see is that reamers tend typically to cut a slightly larger than they actually measure (even the best of the best); and

c. Chamber polishing takes a little more.

The net result is I see fired brass at .200″ forward of the bolt face at .471″ – .4715″ in diameter, so a re-sized dimension of .470″ works.

For day to day resizing I use a 6mm BR Redding Type S FL sizing die with the lock ring set so the die sits up off the shell holder about .100″ from where it would sit for 6mm BR case resizing (i.e. the BRX has a .100″ longer head space than a 6mm BR). To hit the base, I use my 6mm Dasher Redding Type S FL sizing die with a .022″ thick cardboard spacer ring I made under the lock ring, and with the de-capping rod assembly and neck bushing removed. This Dasher die with the spacer seems to hit the base of the BRX case close enough to the web to bring it down for comfortable chambering and extraction, and it keeps the shoulder at around .4585″ – .459″ for re-sized brass (vs the fired brass that measures right around .460″ at the shoulder). When I used a .308 Win die to hit the base, while the base was fine, at the shoulder I was seeing .4565″ – .457″, which was more than I wanted to see. The Dasher die works great, because I have the lock ring set up for my work with the Dasher, and I just remove the de-capping rod and bushing, put the cardboard spacer under the lock ring and use it for the BRX base. A quick do-it-yourself cardboard spacer (anywhere around .022″ – .026″ works fine) can be made from the cardboard that a number of shooting components come in (the cardboard that holds sleeves of 1000 CCI or Federal primers, the cardboard from older Lapua brass boxes, the cardboard from Lapua bullet boxes, etc.).

Robert

By: Robert Whitley

Robert Whitley — Tue, 24 Aug 2010 11:30:53 +0000

Boyd

Funny you should mention that as I addressed the issue you raised in the info submitted for publication, but it was edited out by the publisher (I assume to make the piece short enough to fit in the bulletin). Just remember, a bulletin item is a brief blurb, not a full story.

Robert Whitley

By: Boyd Allen

Boyd Allen — Tue, 24 Aug 2010 05:28:13 +0000

It would be interesting to know what the base size of Robert’s brass was before sizing…don’t you think? One would assume that a knowledgeable designer would build in a little clearance between his chamber and a sized case. If he did, then his chamber is bigger than .470. If it is not, then his die isn’t doing any sizing at that point on the case….not good. Also, this is a twice fired and sized case. As brass work hardens, the amount of diameter reduction, at the base of a case, produced by a given die, will decrease, due to increasing spring back, which means that if you want a die to work at the end of a case’s life, you need more clearance built in than is actually needed for smooth functioning of a new case.