The 6mm BRDX — a Longer-Necked Dasher
At the recent IBS 600-Yard Nationals, the 6mm Dasher cartridge was the most popular chambering for both Light Guns and Heavy Guns. The Dasher, a 40° improved version of the 6mmBR Norma case, can definitely shoot — no question about that. But the Dasher has one less-than-ideal feature — its very short neck. This makes it more problematic to shoot a wide variety of bullet types — short bullets as well as long. In addition, the short neck makes it harder to “chase the lands” over time.
For those folks who like the performance of the 6mm Dasher, but prefer a longer neck, there is an excellent alternative — the 6mm BRDX. This wildcat shares the 40° shoulder of the Dasher and has nearly the same capacity. Like the Dasher, the 6 BRDX can drive 100-107gr bullets to the same 3000-3050 FPS accuracy node. But the 6 BRDX has a longer neck than the Dasher. Depending on your “blow length”, the 6 BRDX will typically give you about .030″ to .035″ more usable neck length. That may not sound like much, but it is very useful if you have a longish (.110″+) freebore and you still want to shoot shorter bullets in the lands for some applications.
Your editor has a 6mm BRDX and I really like it. The neck is long enough to let me shoot 90-grainers loaded into the lands as well as 105-grainers. Fire-forming is pretty easy. I just load very long (so there is a firm jam) and shoot with 30.0 grains of Varget and a 100+ grain bullet. With a Brux barrel, my BRDX easily shoots quarter-MOA, with some 100-yard groups in the ones in calm conditions. This is with a Stiller Viper Action, and Shehane ST-1000 stock bedded by Tom Meredith.
6mm BRDX Reamer, Dies, and Hydro-Forming Service
It’s not difficult to set up a rifle to run the 6 BRDX. Dave Kiff’s Pacific Tool & Gauge has the reamer (just tell him the freebore you want). Whidden Gunworks offers excellent BRDX sizing and seating dies. And if you don’t like fire-forming, give Darrell Jones of DJsbrass.com a call. Darrell can hydro-form 6 BRDX brass and even turn the necks to your specs. Darrell’s hydro-forming service saves you time and preserves precious barrel life.
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Tags: 6mm, Brass, BRDX, Darrell Jones, Dasher, Hydro-forming, PT&G, Whidden
So, what is your reamer’s freebore specification,and how much bullet shank (bearing surface)is in the neck for the bullets that you have tried? With those bullets, where does the front of the boat tail (back of the bearing surface) end up in relation to the neck shoulder junction? Might if be that another advantage of this design is that it makes it easier to keep the bearing surface clear of potential doughnuts? I wonder if the longer neck and sharper shoulder angle will give a little longer barrel life (TP theory).
Editor: Boyd, Freebore is 0.120″ if I recall. Yes the base of the bearing surface on 105gr Scenars are ahead of the shoulder Junction. We had enough neck to shoot 90s and 95s too. The BRDX is very close to the Dasher — just a slightly longer neck. As you stated in your next comment, the shoulder angle is same as Dasher, both are 40 degrees.
Correction: I should have waited for the second cup of coffee to kick in. The shoulder angles are the same.
The Dasher will be hard to dethrone, but I feel that the 6mm BRDX only adds to the Dasher’s short comings if it has any.. How long is Shiraz’s Norma Dasher brass supposed to start it’s life @?
Ray
Ray,
Shiraz told me the Dasher case length will be 1.553″.
I have only the vaguest grasp of what is being discussed. But it would seem that 3K fps would lead to unnecessarily short barrel life, as with early .220 Swift barrels. Any remedy ?