I have a .17M2, and have seen no problems whatsoever with bullet expansion at any range or velocity. Have killed several squirrels, crows and assorted blackbirds with it, and the results are always the same, instant death and a big exit hole. Here are some pics of a squirrel I shot at 110 yards, where the velocity should be down to around 1500 fps. Damage was far less than I would expect with a .17 HMR, but then this is why I bought a Mach 2. http://www.picyard.com/main/data/510/156Squirrel_wound_damage_17M2_004-med.jpg http://www.picyard.com/main/data/510/156Squirrel_wound_damage_17M2_002-med.jpg http://www.picyard.com/main/data/510/156Squirrel_wound_damage_17M2_001-med.jpg
Pictures are of skinned squirrel showing exit wound, unskinned exit wound, and entrance wound (right side).