doublegunshop.com - home Forums General Discussion Double Rifles, Paradox Guns & Gauge Rifles @ doublegunshop.com Best place for a scope on a double

I have read that adding a scope to a double rifle can alter the regulation. From a physics point of view, is there a location that "should" effect the regulation less, such as near the balance point, etc.

Just wondering if this is something that is worked into a rifle that comes with factory mounts.

Thanks

Tom

Tom,
This is just a guess, but I strongly suspect that the closer you have the scope to your balance point, the less it will affect the bullets point of impact. I am currently working on an over and under rifle for a client who wanted a scope incorporated in his new gun. I am regulating it with the scope first. I will then set the iron sights to match that point of impact. It seems to be the rule that if you are going to have a scope mounted on the gun, that you need to regulate it with the scope present.
As soon as I have done both I can tell you more about the affect it has on the points of impact by removing or adding the scope. I am also fairly certain that because of the rotation in a side by side, this effect will be worse on them that the over and under. Also his scope is a lightweight red dot which probably won't affect the gun as much as a heavier scope would.
You also bought up a good point about factory scope mounts on rifles. If you will notice, they all set them as far back on the barrels as possible, probably so the scope will be as near to the balance point as possible.
Bob H.

Thanks Bob.
I was thinking about everything that went on when a double was fired and it looks rather complicated. The balance point seemed to be a good place to start, but the rotational issue starts at the butt. In addition to that, the recoil from both barrels is different.
Regulating it with the scope on seems to be the best way to go. Let us know how the over under works out.

Thanks
Tom

Tom:
Recoil "rotation" may be influenced mostly at the butt, but I am talking about is lateral rotation or rotating around the center of mass which runs right down the middle of the side by side double between the barrels. When you fire the right barrel, the gun recoils upward but also trys to rotate counter-clockwise when viewed from the butt end. The reverse is true for the left barrel, it will try and rotate clockwise. The fact that the gun is against your shoulder can not compensate or stop the rotating completely.
Early on when I started making rifle conversions, I got the bright idea of machining two laser pointers to just go down each barrel at the muzzle and superimpose them on an object across the street from my shop. When I had that accomplished, I made up the correct spacers and soldered them in, thinking that I had achieved the ultilmate in rifle regulation. But when I shot the gun, they were nowhere close to right because of the lateral rotation or twisting of the double.

Because the bores of an over and under rifle are stacked one above the other and in line with recoil., you don't have the twisting rotation to deal with. I had suspected this but had not confirmed it till I actually got to doing a double stacked barreled gun. What think will affect the point of impact is weight added to any place other than the center of mass such as a heavy scope and mounts. How much this affects it, I don't know yet, but I will soon. I will tell all of you this though, the heavier the bullets and bigger the bore, it seems like to me, the less the point of impact is affected. The big heavy bullet rifles tend to be much easier to regulate than the smaller lighter bullet rifles. Also the bigger bores are more forgiving of bullet weight and speed changes in loadings. Bob H.

When you install a scope, the effect is a increment in the "system weight" (and inertia), the heavier the scope and mounts the bigger. Your rifle will be heavier, and with the same force trying to move the shooting barrel, the net result will be your SxS double will cross the shots a little more. The magnitude of this change will depend of many factors, of course. In my own Merkel 150 9,3x74R, with 250-260 grains bullets, the rifle will cross the two shots 1-1,5" al 50 metres. Hope this will be useful.