Should the 6.5mm-08 (260 rem) be 1 in 8" twist or 1 in 9 twist? If 1 in 9 is the defacto standard I take it that the 1 in 8 would tend to shoot the heavier bullets a bit better is this true? If so - what would be the lightest bullet weight one should use in the 1 in 8" twist barrel assuming a barrel length of lets say 24"?
A lot (most?) people shooting long range and/or the long spiky VLD-ish bullets from a 6.5 whatever seem to tend to go w/ an 8 or *maybe* an 8.5 if its a hot rod. I think the 9 is more common on hunting rifles, carbines, etc. where extensive use of long 140+gr VLD's isn't really expected. That said, there are some 140gr 'hunting' bullets like the 140 SST from Hornady that are pretty VLD-ish in ballistics! I don't think (based on the use of 107/108 and 120/123gr bullets in competition by myself and a lot of others) that the lighter bullets are going to be adversely affected much by the slightly faster twist. It's not like going from a 1-14" to a 1-6.5" in a .224 caliber; not near as drastic a change. I'd err on the slightly fast side to make dang sure you are able to stabilize the heavy bullets; the lighter ones will most likely shoot just fine.
Hmm I guess it would seem then that a 26" or 24" barrel of twist 1 in 8.5" would be good and offer more versatility as far as loads are concerned. I suppose the average weight of the loads I would use is 120gn, but would like the ability to load like 85-142gn bullets for a bit extra versatility, I understand this might not be possible - ill ty contacting shilen and hart and see what they say, I just want a wide variety of loads available. Heard alot from a few cusom shops who say that the use of light bullets in the 1 in 8 can cause overstabilization issues resulting in poor accuracy due to bullet yaw. was thinking of compromise with 1 in 8.5" but not sure -- any comments/ suggestions?
I just touched on this subject in my reply to the 6.5x55AI thread in this catagory. I have both 8 and 9" twist barrels for my BR guns. The 9" twist will handle everything except the 155gr Sierra, Clinch River VLD bullets in cooler weather. FYI: My barrels are 30" and velocity is 2900fps + with all bullets. Some say it's iffy with the 142gr Sierra also in 9" twist, but I've shot some decent groups and scores with them in cooler weather. The best combo I ever shot was a 9 twist barrel with the 2000 Lot# of Hornady 140 A-Maxs. Sure wish I had more of that Lot#. Once I switched to the 2001 Lot# I had it never shot good again. Had to back up and abandon the A-Maxs because the newer lot# would not shoot period.
The most popular twist for the 6.5 shooters in the BR game is the 8.5" twist hands down and that will handle the 147gr Clinch River bullets.
Think about the type of bullet you are mostly going to fire and consider the throat needed to properly shoot that bullet. There would be a lot of compromise needed to throat something to fire anything from a 120gr to 147gr bullets. You will need to step on one side of the line or the other right now.