Good question, Quackster. I was trying to get JT to answer this same question on another thread, but so far there is no response. Personally, I don't think there is a difference in a certain mass of mercury and the same mass of another weight such as steel or lead. JT apparently thinks the mercury is better, but I think it could actually be worse if the tube is not completely (or nearly completely) filled. The reason I say this is that if the tube is not full, the gun could fully recoil into your shoulder before the mercury sloshed to the other end of the tube to offer any (or much) resistance.
Actually a mercury recoil reducer works two fold. They add mass to the gun and this will reduce the recoil energy of a gun weather the mass is a liquid or a solid. Also since the mercury is a liquid sloshing around in a tube when you fire the gun the mercury does not immediately accelerate with the rest of the gun it remain at rest. Then as the gun moves reward the mass of mercury runs into the muzzle end of the tube it is contained in. This delayed acceleration of the mercury mass does not reduce recoil energy when compare to a gun with similar solid weight but the delayed acceleration of the mercury lowers the magnitude and lengthens the recoil impulse. This will make a sharp recoil feel more like a big push.
I have been shooting a lot of trap this fall and put one on the magazine cap of my BPS. I was really after just adding some weight to the barrel to help me smooth my swing out, but figured I would try the mercury recoil reducer. It added the 1/2 lbs I wanted and I do think the mercury did make a difference more then just adding mass.
The mercury works in both ways as added weight and as a damper as it's a liquid.
Its fluid dynamics, for the same reasons that they have baffles in tanker trucks and the that a raw egg will not spin like a top and a boiled egg will, or that a compass needle floats in a solution of oil. The liquid is able to damp the forces.
I am glad this question was asked.. because I was wondering how it actually worked for some time now. I would think sites like Benelli.com would have more information on it.. since they sell it for their guns.
Some additonal questions that come to mind:
- How safe is it? Mercury as we all know is not good for us.. or the environment. Can/do they break?
- Are other liquids just as effective?
- Is there any difference if it is added to the stock or to the forend of the gun?
Take a look at the description for one of the many that are on the market, I happen to have the one that fits in the barrel and I place it in the top barrel when shooting singles trap in my Fabarm O/U.
Mercury is used because it is a dense metal that is a liquid at room temps. I'm sure you could concoct a sand and oil mixture or plastic beads and oil mixture that would act similar, but mercury is readily available and not likely to be as temp dependent as some of the other possible creations.
The containers that it comes in are well sealed, I'm sure if you wanted to you could hacksaw into them, but I've dropped mine a time or two and no silver liquid has come out.
You can get a similar effect from just adding weight, but that is just working on the principal that it requires more energy to move more mass, so there is less felt recoil. More energy is used with the sloshing of the mercury.
Another option is something like a Deadmule http://www.brownells.com/aspx/NS/store/ ... IL+REDUCER this contraption is a spring that counteracts the recoil force, similar to a shock absorber. Also something I happen to have, this in another gun that was heavy enough to start with, but as I have an old shoulder injury from stopping a 12ga slug I try and limit recoil when I can, most of my long guns have at the bare minimum aftermarket recoil pads.
As to were you want to put the weight, well that is more about personal preference, there are mag caps that have extra weight to them, there are barrel mounted rigs that allow you to position the weight were it best serves you far forward for barrel heavy or father back for a lighter feel, you can put them in the magazine, the stock, in one of the barrels....its where it best balances out the gun for you.
Look at some of the new bows on the market with the internal shock dampeners, small brass disks held in place by some rubber, the vibration is spent shaking the brass disks around.
There is all sorts of physics involved when shooting...more than I can remember from either high school or college physics.
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