I've got a Ruger No.1 RSI with 20" barrel as well. I'm getting chronographed average velocities of 2869 fps with the 140 gr. Sierra Pro Hunter with 51 gr. H414 and 2621 fps with the 160 Sierra HPBT over 52 gr. IMR 7828SSC. Both these loads are extremely accurate - consistently gives 3 shot one-jagged-hole groups at 100 yards. As far as muzzle blast, it's not bad at all, and you don't get much closer to the muzzle than with the No.1 RSI (36.5" overall length). Nothing at all wrong with a 20" barrel.
JW
