Well done guys, I'm happily surprised! As something that very few people have an opportunity to ever see, for two people to ID it so quickly is very good. Ordman has it, though he was actually beaten by a couple of hours in a PM sent by Spotter.
It is in fact a section of the burster tube from the MK116 Weteye Bomb, designed to be filled with GB nerve agent. I've put the original photo back up, plus a blow-up of the stencilled markings. (photo 1&2)
It is a multi-linear shaped charge as noted by several, and BombsAway was pretty close with his guess of a BLU-85 (photo 3). Here are a couple pictures of the bomb as well. (photo 4&5)
In response to Ordman's parting question about the Weteye Bombs that remained after Rocky Mountain was closed - "Wonder where they are?", the remaining bombs were transferred to the US's largest CW storage depot in another of the Rocky Mountain States. They were declared to the OPCW under the Chemical Weapons Convention in 1997, and have since then been monitored and destroyed under the terms of the treaty, verified by the constant presence of OPCW inspection teams. With allowed exceptions (empty training examples and displays may be kept), they no longer exist.
Well done to all - we'll do it again another time. JO