I have both a 260 and a 6.5WSSM.
They are virtually identical with a couple of exceptions.
To me the 260 is much more tolerant of load variations.
The 260 is a Savage 110 action, 26" Shilien 8 twist match barrel. I am loading them to what Quickload says is very near max for the 260, a 140 Berger over 47.5 grains of H4831SC at 2868 fps, at like 60K PSI. (max load, don't use this as a starting point!)
The Remington brass is holding out ok, but was stretching some and I had a few split necks. No pressure signs at all on case head, primer pockets, or bolt lift. Adjusted the headspace on the seater die and hopefully that will help the stretching.
They are shooting 3/4" to 1" at 200 yds.
I also have a 25 WSSM barrel that I swapped out for a 26" - 6.5WSSM barrel chambered by Pacnor, 8 twist, canted lands, match barrel, etc. This is built on a Savage 16 WSM action. Feeds fine from mag.
I am shooting 140 AMAX over 50 grains of H1000, very close to a full case, also into the 1" group size at 200. It is at 55K PSI and 2837 fps according to QL, which is low pressure for this case.
I find that H4350 and H4831SC do work well for the 6.5WSSM, but you go from no pressure at all to a sticky bolt in a very small change in charge weight. I find the WSSMs to be very peaky and somewhat difficult to load for ...(someone chime in and help me ...)
I am positive that if I had a different scope and more practice I could get these groups down further as it is obvious to me that I am definitely a big factor in the group sizes. (I am thinking 8-32 power with tiny target dot may help ..)
As far as the short barrel goes the 260 has a case capacity of 53.5 gr H2O and the (25WSSM based) 6.5WSSM also has a case capacity of 53.5 gr H2O according to QL. So from that I see no difference in the short barrel assuming you could make faster powder work ...
The thread on 6.5-06(AI) was very interesting as far as info on 6.5 caliber options. Also, Jerry wrote some stuff on a 6.5 Mystic that was interesting to me. You could search for this stuff.
When it comes down to it, the 6.5x284 is probably one of the better choices if you want a fast 6.5. There are very high quality components available for it and lots of documented success by the benchrest crowd.
I think a 6.5WSM would be an interesting choice, so far I have seen a 6.5x300WSM and 6.5x270WSM to chose from as far as existing reamers. I was thinking that if one did a 6.5x270WSM you could use 270 WSM brass and 270 WSM Redding bushing dies with 6.5 bushings like I did with the (25WSSM) 6.5WSSM. From what I hear a 6.5WSM should be very similar to a 264 Win Mag...
(A 6.5 RSAUM would be cool also, I have not heard of anyone with a reamer or dies for one.)
I really like the 260, it is easy to load for, has almost no recoil, long throat and barrel life, and is able to shoot very high bc bullets at reasonable velocities to get way out there ...
Have fun deciding which to go with ...
Hope I didn't ramble too much.
If it is a slow twist and wants to have the lighter bullets, maybe I can run a little hotter chambering?
