300 RUM for Varmints...

[crankshaft]

I want to build a new rifle for groundhogs and coyotes and would like to build a 300 RUM and use 125gr's or 110 V-Maxes. Probably won't be shooting no more than say 400 yards. Has anyone used something that light in a Ultra? Would kind of velocities could I expect out of a 26" barrel? Would like to get as close to 4000fps as possible. What other options are available with that kind of speed? How about the 223/243 WSSM's or 22-250AI? Just would like to see what other people use for speed.

Thanks