They might use actual amputees from the army. I know a dude who got his leg blown off in Belfast by the IRA and he's still in the army and he like does a lot of extra work in war movies as "some dude in the background with his leg blown off." Hats off you know that takes some balls to want to relive that situation again and again. Its pretty rad he actually gets a lot of work and occasionally I'll spot him in the background of movies all squirming around and bleeding. He was working on that HBO series about Feudal England for a while apparently. I guess he also trains people to be more convincing dying people in movie scenes like explaining the actual psychology behind it and such.
That shit looks like so much fun. Like the most gnarly game of paintball ever.