Arms on tools?

On certain tools your arms are in different places, like with a sniper, your left arm is along the barrel of the gun not at your side, how would you do that on a gun, I have looked at free models to no prevail, i'm not necessary requesting a script but more asking where to start, maybe some Wiki pages, etc.

To do this, you have to use Welds. Try this page.

Maybe try the wiki's changing default character animations. I haven't really looked at it all that much. But I hope it can be of some use.