Google 50 cal dreamer
Its a small steal device, (mine is about 8 inches long, newer ones are a bit longer), used to render safe, (disarm) bombs;
The bullet is pulled and something stuffed in to keep the powder in the case. The case is fired either electrically, or with a small piece of det cord.
In place of the bullet, it fires water, nickle powder, or a steel slug. I wont say how its used, but when fires, the dearmer flies back wards for a while.
I normally tape the wire used to fire the armorer to the armorer itself plus put a long ribbon of engineer tape so I can find the dearmer afters it fires.
If you ever saw one fired, you'll know why there is not 50 cal BMG pistols.