I have a mrecury tube in the stock of my 500 NE Ruger #1. It slipped right in the factory hole for the attachment bolt. (I added 1.5 wraps of electrician's tape to insure a snug fit)

Quite honestly, I do not see any reduction in recoil when using a mercury tube as compared to using a homemade weight tube contructed of copper pipe, epoxy, and small shotshell shot.

I've tried the 500 with both systems and I cannot feel any kind of dramatic difference.

Balance seems more important with regard to felt recoil, especially if you plan to shoot from a bench at all for load work.

Whenever I modify a rifle for balance, I place the arm upon a homemade stand with a fulcrum that allows me to add various weights to the rear of the stock until I determine what weight I need to achieve the balance point I desire.

I start by adding long fishing weights. They are pliable and can be placed upon the stock easily. When I need lighter ballasts for fine tuning, I use little rice-filled zip lock bags. (the kind you get little gun parts in from suppliers) Once the rifle balances where I want it, I weigh all the fishing weights and rice bags to get a total weight for my plug.

Once I have determined the amount of weight I need to add, I build a plug using the copper pipe method. I take a 4 or 5" piece of this pipe and place it on my scale with a piece of waxpaper separating the two. I have already pre-weighed my shot and pipe to get an idea where I'm at. I also weigh an appropriately sized nut that will be added to facillitate removal of the plug for disassembly if necessary.

Pour a little epoxy into the pipe and let it settle to the bottom. (the pipe is standing on end against the waxpaper on the scale.) Place the nut aside but on the scale so it's weight is included. Now add a bit of the shot followed by more epoxy. Gently tamp with a small dowel or other tool to compact and disperse the shot amongst the epoxy. Keep going until you near the top where you will be adding the nut. Coat the inside threads of the nut with wax or whatever light grease you have available so the epoxy doesn't violate the threads. Insert the nut into the end of the pipe and finish filling the void with straight epoxy. Your finished tube should be very close to your target weight. Carefully remove the tube from the scale, set aside and allow at least 24 hours to dry. Longer is better as this adhesive is in a very dense form with no atmosphere to allow solvent release which is necessary to the curing process. I generally wait 72 hours just to be sure.

If the pipe you have used is slightly loose in the stock hole, the electrical tape will work fine as a fitment shim. Use a wrap at each end to avoid binding. And.... be sure to install the plug with the nut staring you in the face so you can use a long bolt to remove it in the future if you have the need.

The process is easier than it sounds, just a bit time consuming. I've balanced most of my arms now and I'm so pleaased with the results I question my sanity for not doing it sooner!

Good luck and feel free to query further.