what is the right way to install a mercury tube in a rifle. I have never installed one but I'm thinking of putting one on my 458

i assume you mean in the butt stock.
it is not for the faint of heart. here is how i do it.

remove the pad/ plate on the gun. determine where it will fit. closer to the centerline the better in the upper third of the butt stock if possible. mark the stock and drill a small,1/8 inch hole about 1/4 inch deep.

most tubes are about 3 inches long so get a 6 inch long 1/8 inch drill. put the stock in a vise level and using a hand drill drill the hole about 3 inches deep. put a small washer on the drill shank. as the bit turns it will migrate forward if you are pointed down and back towards you if you are pointed up. let the drill cut, don't force it, and clean out the chips often.

after your pilot hole is drilled use a sharp spade drill bit to enlarge the hole to the right size, just a tad deeper than the tube is long. let the point follow your hole. i saturate the hole and end grain with polyurathane to seal it.

put the tube in after the poly dries, make sure the threaded hole in the tube is visable and facing out. i cut a small piece of closed cell foam to put oner the tube to hold it in place under the pad/plate.

I put one in my Ruger #1 450-400. It made the rifle quite butt heavy, but not in a bad way. It had a hole in the butt, about .050 too small, so I turned the reducer down. That was easier than trying to enlarge a hole. What rifle do you have? The C&H reducer I have is 5 inches long, .884 OD, and weighs one pound.

inline with the bore or toe .. put a wooden cap over it, zro running room .. can be scary

dpcd,
I have a remington 798 in 458 win mag