How does a beer gun work?

Kind of a newb question...Is this how I get my kegged beer into bottles w/o going flat? A counter pressure type thing?

THanks!!

P.S. I tried search and didn't find anything

I don't know the specifics. I do know that it's very simple to use. I just hook my beer gun into my CO2 from my regulator and then hook it into the liquid out on my keg. You can them use the beer gun to purge the bottle with CO2 gas by pressing it one way, then press it another way to empty the beer from the keg into the purged bottle.

If you can find a copy of "Brew Ware" (I have it checked out of the library), it has details on how to build your own.

The theory is: You have three lines and three valves. One goes to your CO2 tank, one goes to the fluid out on the keg, and one goes to an overflow bucket.

You open the CO2 valve to equalize pressure with the keg, then open the fluid valve to allow beer to fill the bottle. You close the fluid and CO2 valves, then open over flow valve and remove the rig from the bottle.

If you break the seal before you release the pressure with the overflow, you get a shower.

I saved my $$ and have a BMBF! It works great...and I'm going to use it again tonight!