Originally Posted By: 6mm06
What barrel twist is recommended?
That depends on your bullet choice. There has been a bunch of research and development on this, by several groups, and most of them live on, or visit, the 6.8Forums. But to condense it down, results show the 1:11.25 twist gets the most velocity out of typical bullets(85-110 gr), with good stability. The 1:10 twist barrels came from the .270 Win. chambered hunting rifles, shooting the typical 130 gr, to 150 gr, bullets. In the 6.8 SPC, most of the bullets chosen are between 90-110 gr, so the 1:10 twist is faster than it needs to be for the shorter lighter bullets, and that increases pressure, unnecessarily, and ultimately lowers potential velocity of lighter bullets.
I have both a 1:10 twist RRA upper, with a SPC II chamber, and a 1:11.25 twist ARP barrel(DMR chamber) on a home spun upper. Both put 90-95 gr. bullets into tiny groups, but I do see signs of pressure sooner in the RRA barrel, and less velocity. Most of my loads are for accuracy, so they aren't pushing max. loads. I do shoot them in both rifles, just in case one of my sons, or grandson, end up with the rifle, and "Grandpa's Ammo". The RRA upper will show flattened primers, but no extractor marks, for a couple of the warmer hunting loads.
If I were shooting heavier .277 bullets(130-150gr), then I would stick with the 1:10 twist, to insure good bullet stability, and live with more arch in my ballistics.
One side note. Barnes came out with a 95 gr. Tipped Triple Shock bullet, targeted for the 6.8 SPC. IMHO one doesn't need the heavier traditional .270 Win bullets, to get excellent on game results with the little brother to the .270 Win.
Squeeze