Adding Springs To Magazine And Stock Weights


Hi, Bruce.

If you wouldn’t mind, how about reading this thread and giving your opinion, either publicly or privately. I know, I may have re-invented the wheel, again…

(The thread refers to setting up spring buffered weights in the magazine tube and stock of an 870 in order to reduce recoil.)

Thanks,

Dave
Jr Technoid in Training…

Dear Dave,

I read the thread. Great minds think a like. Been there. Done that. I’ve tried all sorts of weights here and there in pumps and autos. Here’s what I’ve learned:

1) adding weight of itself reduces recoil on about a 1:1 basis. IE, if you add .8# to an 8# gun (10%), you will reduce recoil by more or less 10%. It’s not linear, but it’s close. This is totally independent of whether or not that weight is moving. The SAAMI formula for free recoil does not take into account the length of the recoil pulse. It just calculates the area under the recoil curve.

We all know that duration of the recoil pulse is also important because that’s how autos feel softer than pumps. The SAAMI free recoil formula does not calculate this.

2) The whole idea of the Edwards and various valved mercury reducers is not only to add weight, but to alter the timing of that weight shift. This is sort of a double whammy. I don’t have machinery to calculate the spreading out of the recoil pulse, so I can’t quantify it, but there’s no doubt that an auto or a gun with a hydraulic stock SEEMS to kick less than one without those features. So, in theory, adding weights with spring buffering to permit them to shift rearward a moment after the main recoil pulse is a good idea.

3) You do have to be careful how you set up your springs. When dealing with the magazine tube weights, if the springs are to the rear of the weights, they don’t really do much except hold the weight in place. If those leaded shells are loose in the magazine, inertia will hold them in place while the gun moves rearward on firing. This will put a tremendous hammering on the front of your magazine tube. I blew the front cap out of a Model 12 doing this. I would suggest a spring of some sort IN FRONT of the magazine tube dummy weights. This will A) keep your magazine tube from getting hammered, and B) stretch out the recoil pulse due to the delayed movement of the weights caused by inertia. A spring BEHIND the weights does not do this. As a practical matter, you will end up with a spring in front and also behind the magazine tube weights. The issue then becomes one of damping the oscillations, if you find that a problem.

4) Ditto the weight in the stock. Here you can certainly pack it in place without damaging anything. You will lose the elongation of the recoil pulse, but you will still have the benefit of the added weight. If you do choose to use a spring, you need one in front of the weight for the reason above. You’ll also need one behind the weight to keep the weight from beating the butt plate into pieces.

The way I ended up doing my trap guns was to use lead plugs in the magazine with springs in front and behind. In the stock, I just wedged the lead in so that it couldn’t move and didn’t try to set it up on springs. That way I could get more lead in.

Are the springs fore and aft of the lead in the magazine tube worth it? I don’t really know about reducing recoil any more, but they did keep me from damaging the magazine tube again.

Best regards,
Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)
<http://www.ShotgunReport.com&gt;

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