Re: .260 round and competition.
I doubt you'll have subpar velocity issues with a 22-24" barrel. As long as you can get a 142SMK up to 2400fps, you'll still be just under 1200fps at 1Kyd, altitude 1000ft. Savage 24" barrel made 2900fps with a max/overload charge of 139 Scenar/40(41?)gr V-V N550, 2700fps is neither unreasonable nor difficult to achieve. Hodgdon specifies a load of 37.5gr of Varget delivering 2645fps in a 'rifle barrel' of unspecified length. My 28" uses 43.8gr H4350 to get the 142 up to 2850fps. That's a moderate load, but I think the powder may be a bit slow for a gas gun.
I doubt you'll have subpar velocity issues with a 22-24" barrel. As long as you can get a 142SMK up to 2400fps, you'll still be just under 1200fps at 1Kyd, altitude 1000ft. Savage 24" barrel made 2900fps with a max/overload charge of 139 Scenar/40(41?)gr V-V N550, 2700fps is neither unreasonable nor difficult to achieve. Hodgdon specifies a load of 37.5gr of Varget delivering 2645fps in a 'rifle barrel' of unspecified length. My 28" uses 43.8gr H4350 to get the 142 up to 2850fps. That's a moderate load, but I think the powder may be a bit slow for a gas gun.