there is a button at the top of the screen that says reload click it to reload
When th ammo in the sentry gun reaches 0, then you can reload it. To reload, walk on top of the sentry gun and press the F key. I'm not sure if you can reload it when there is still ammo in it though, but you can try. When you reach the rank Colonel, once you set up a sentry gun, you will have double ammo for the sentry gun, and you can reload it faster.
there is none only on siftheads world act 1 2 3 4 5 6 those are the only siftheads games you can do it in
shoot outsid the screen that should reload your gun.
Chamber
you have to get the USP pistol and empty the clip and when you reload it will "flip" the gun
default is R. goto options keyboard and look for reload key
you cant
space bar
Yes, the operator does it.
It is a game that you play
?