www.students.dsu.edu/coxs/ballistics.htm

"A mercury tube can also be installed into the butt of the rifle. This is a tube about the size and shape of a cigar. The tube is filled about halfway up with mercury, and acts as a shock absorber. A hole is drilled into the stock, the tube is inserted and held in by the recoil pad. This tube costs around $40, and costs about another $20 to have a gunsmith do the work. The angle the tube is installed into the stock will make a difference; I recommend breaking down and paying a 'smith to do the install. The downside of the merc tube is it weighs around 8 ounces; it will alter the balance of the rifle (may or may not be a good thing), and it increases the weight of the rifle."

Any feelings about this?
Thanks,
CardiacDoc