If I were going to spend the time & $$$ to set up a 223 tubegun, I'd most certainly go with a 1-7 - 1-7.2tw bbl throated for the Berger 90VLDs. I feel the Sierra 90s have too much bearing surface to allow them to be pushed to competitive velocities without getting into too much pressure. In the first place, they were designed for use in AR15s, so the design wasn't optimized for use in a bolt rifle. I set up a 30" Bartlein 1-7.2tw med Palma bbl for my R5 tubegun, throating it for the Bergers, and have seen velocities in excess of 2900fps out of it, which makes the rifle very competitive with a 308.
I've had excellent results in AR service rifles back in 2002-2004 with JLK 90VLDs out of PacNor 3-groove 1-6.5tw bbls, but when we discovered that slightly slower twist bbls would easily stabilize 90s, we dumped the 6.5tw bbls. The last one I had blew up everything I tried in it in XC HP matches, including Sierra 69 & 77MKs, as well as JLK 80VLDs.
I've had excellent results in AR service rifles back in 2002-2004 with JLK 90VLDs out of PacNor 3-groove 1-6.5tw bbls, but when we discovered that slightly slower twist bbls would easily stabilize 90s, we dumped the 6.5tw bbls. The last one I had blew up everything I tried in it in XC HP matches, including Sierra 69 & 77MKs, as well as JLK 80VLDs.
