Took me only 2 tries to get it right.  What a ton of fun!!!  Sure did blow through a lot of ammo though.  Now I have to replenish my stash.  The rifle sure did get plenty hot as well.  Will there be any harm done to the rifle if I stop shooting it only when it gets too hot to hold?  Should I stop shooting it prior to it getting that hot?  Also, if it gets that hot, will dunking it in water (minus the ammo) hurt the rifle at all? I shoot with a buddy of mine who is a former Marine and I see him often dunk his rifle in the lake to cool it off.    

And what, again, is the purpose of this?  Oh, too much ammo I guess.  Next time send it to me and I'll put in thru a target!  

Only half joking.  :-P

Are you bumpfiring an AR or an AK ?

I don't think you're gonna help the rifling any by overheating it, but I've bumpfired quite a bit through my AK's and they still shoot like new...
I even melted a set of synthetic handguards, after bumping off a whole 100 round drum...No harm done, just replaced them with bakelite & alumium...

As far as dunking the gun in water when it's hot...
Thats a NO-NO...The quenching of super hot metal in water, hardens it and makes it brittle...  
Also, it could easily bend the barrel...
I just lock my bolt open and stand the gun upright. Heat rises, and creates an updraft, cooling the barrel quicker...(works for me)


Just my $.02