Re: 6.5 140 Hornady SST
Well, this is a little bit of BTDT (been there done that) for me. When I got my rifle barreled, the main reason I went w/ a 30" is that a screamer of a deal fell in my lap. $300 total for a couple sets of dies, about $150 worth of Lapua brass, about $100 worth of bullets, *and* the barrel (takeoff from a switch barrel after 600rds -- the guy liked the other barrel too much to use this one any). Otherwise I probably would have gone w/ a 26-27" as that is more 'normal' for the game I'm playing in.
I kept digging up all this load data on the 'Net, most of it w/ no velocities listed. The loads shot well, and so the shooters didn't really care if it was going 2650 or 2850. The few I did get speeds for showed such a huge variance it wasn't even funny. Either there was some 'slow' / 'fast' barrel stuff going on, or some decidedly different takes on how much pressure sign was 'too much'.
Figured that since I had a 30" barrel, and almost all the speeds I was finding were 2800 max from a 26" barrel for a 139-142gr, or 3150 for a 120-123gr, I should be able to hit 2850-2900 easy for the 140's and 3200-3250 for the 123's.
I've pretty much ran into a wall w/ the 123's. Pressure signs start getting awful hairy around 3150-3175. A part of that was a loading error on my part (seating depth), but since then I've spoke w/ some people w/ a lot more time behind a .260 than I and it appears I was pretty much hitting the limit. I may try some different powders just to see what I can see, but I'm not holding my breath. 3050-3100 is pretty competitive as is, and a lot easier on the cases.
For the 140-142gr bullets... I got up to 2940fps w/ a 142gr SMK, which is supposed to be a tad slower than some other bullets just due to a longer bearing surface. Pressures were getting pretty sticky (I'm a card-carrying member of the sticky-bolt club in my varmint rifles, but for my competition guns I tend to back off a tad) even w/ a extended bolt handle for extra leverage. 2800-2850 I can do w/o any problems, and after reviewing the ballistics for both, the extra speed buys me maybe one click on a 1/4 MOA sight (irons or scope) at 600, maybe 2 at 1K. Not sure thats worth it.
All that said, I recall one fellow who went from a 24" factory Savage .260 barrel to a 28" Lothar-Walther barrel and was getting some (comparatively) astronomical speed. Dunno about case life, etc. Basically decided if I wanted 6.5-284 speed (2900-3100fps) out of a 140gr 6.5mm bullet, I'd probably have to get a 6.5-284 to do it.
Anywho, more power to you if that barrel can really produce that much more speed.