Re: 260 AI speed question
Hornaday list several loads with a 140 grain bullet. All maxed out at 2700 fps using a 24" barrel in a 700 Remington. Hornaday does not list pressure specs, and this is all important. Accurate does list chamber pressure specs on all their loads, and the max SAMMI pressure is 60K psi. AA also used a 24" barrel in an H S Prec. rifle (similar to a 700 Rem.) Here's what they got with a 140 grain bullet:
SWF 140 SP, 41.5 grains of AA 4350 @ 2670 fps with 58K psi
Speer 140 SP, 41.0 grains of AA4350 @ 2669 fps with 59.6 K psi
Nosler 140 Part, 42.5 grains of AA 4350 @ 2733 fps with 59.4K psi
SRA 140 SBT, 43.5 grains of AA 4350 @ 2740 fps with 59.1K psi
HDY 140 SP, 43.5 grains of AA 4350 @ 2740 fps with 60K psi
SRA 140 HPBT, 43.0 grains of AA 4350 @ 2767 fps with 60K psi
SRA 142 HPBT, 43.0 grains of AA4350 @ 2744 fps with 60K psi
Now you may notice I only used AA4350 data. AA3100 often gave higher velocities, but often less than 15fps. Plus 3100 is now extinct. 2700 shot pretty well also, but AA4350 showed at the top almost everytime. I was surprised that they showed no loads using 2495 and maybe even Magpro. 2495 was developed for the .308 case, and works very well. I'd be interested is what 2495 and Magpro would do with the 140 grain class of bullets.
Looking at the improved designs, I can see maybe a grain and a half gain in power capacity. Without much of a serious gain, and less than 100fps the advantage just doesn't show. Plus I suspect some of those wild velocities are approaching 70K psi, and looking to send you to the trauma ward.