Spray it in from the breach end, put a towel or other over the muzzle and press til it comes out the other end. I leave it in for a good half hour, but for really stubborn copper I'll either do it a few times, cleaning with a patch in between. I have also left it for a couple of hours with no ill effects as well. You'll know when it is getting at the copper, as the foam will start to liquify and run out the muzzle with a blue tint. I always have the muzzle end slighlty lower than the breach (propped up at the buttstock), that way it doesn't run into the magazine or trigger group. Hope this helps.
That reminds me I've got to try and find some more. WSS in Calgary used to have it but the salesmen that sell the guns, must not think people want to clean them. As they don't (as of a week and a half ago) have any solvents at all on the shelf??? I actually asked a guy, and he raced me over to the empty shelf and said "right here", but the 4 foot section of shelf was literally bare...