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Vol423 Offline OP
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If an exceptional gunmaker were to produce his most perfect set of barrels, what would the convergence pattern be at various distances? Would the barrels shoot closer together until they reach their convergence distance, then cross and spread apart at longer range? What would that ideal picture be at 10, 20, 30 40 50 and 60 yards? What is the optimum convergence distance for a 12 gauge upland gun?

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Can't answer that, but, I know that the 303s on a Supermarine Spitfire were set to 300 yards.
Wouldn't "optimum convergence" be a bit of a moving target, pardon the pun? I suspect it would differ a bit between a gun primarily intended for pursuit of ruffed grouse in eastern MN/western WI, versus a gun primarily used for pass shooting sea ducks of the coast.

Best,
Ted

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The book L C Smith Plans & Specifications gives the convergence of 12 & 20 ga FW bbls.
They are listed as follows;
12ga
Bbls comverge at the rate of .0113" per inch or an angle of 0░38'.
For a 30 bbl having a 1.156" spacing of C/L's at breech & .8175" at muzzle the axises of the bores would converge at 72.452" from the muzzles. At 40 yard the would be separated by 15.453". These Axis lines would of course cross after passing the convergence point.
For the 20ga with 28" bbl the convergence is given as .011" per inch, a convergence point @ 63.09" from muzzle & seperation of 15.146" @ 40yds.
Understand this is simply where the bbls are "Pointed" this does not mean this is where they are going to hit when fired.


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Originally Posted By: Vol423
What is the optimum convergence distance for a 12 gauge upland gun?


Well, lessee. What is the exact distance at which all birds are shot when upland hunting? And to complicate it further, what exact load do these upland hunters use? Can't have loads of differing recoil, now. It will mess it all up.

I kill all my doves at exactly 22 yards, as incomers, using a 20 ga. with 2 1/2 - 7/8 - 7 1/2. I shoot all my quail going away at exactly the same distance, so this should be easy, eh? All we need now is that exceptional gunmaker.

No, wait. I think I want my right barrel to hit dead on at 22 yards, but my left to be on at 38. And I think I want the right barrel regulated with the 7/8 oz. load and the left for a 2 3/4 - 1 oz. load, which means the angles of convergence must be different.

Oh, bother! Maybe I'd be better off just letting that gunmaker build it like he wants to.

SRH

Last edited by Stan; 05/04/13 07:21 AM.

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The old time gunmakers were just as opinionated and stubborn about their ideas of convergence as we are today. Each maker had what they thought was the proper amount of convergence built into their guns. From shooting huge amounts of shells at pattern paper, I can deffinitely tell you that upland guns were set to converge somewhere between 20 and 25 yards, but heavy waterfowl guns were meant to converge at 40 yards or more. There was really no set amount of convergence rate.
The rates listed for the Feather Weight L.C.'s is certainly correct, but that doesn't refleck on any other guns or makers. As stated before, that just tells you where they are pointed while at rest, and has nothing to do with where they will be pointed at the moment the shot leaves the barrels. The points of impact have to do with many different factors such as the load being fired, the weight of the gun, the length of the barrels and the amount of time the load is in the barrel,the general build of the shooter,etc. As you can see, the gunmakers were working with averages, for the loads fired in their guns, the expected game, and the antisipated distance that it would be shot at, and the general build of the people who were going to buy and use one of their guns.
I think you know that there is no one answer to your question, but this just touches on some of what affects the shot placement and convergence problems faced by gunmakers everywhere. Bob

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Miller's post tells it all. Shotgun barrels, about an inch apart at the muzzle, do not converge. They go out straight as arrows, an unmeasurable one inch apart. If even a minute convergance is built in, as in Miller's example, the patterns are feet apart at longer shooting ranges. Can any of you measure an inch of difference at the pattern board. I can't.

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I had always heard convergence at 40 yards was standard. Parallel barrels that never cross is for double rifles only?

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Actually, it's my understanding that double rifles are built to converge. Usual range, I think, is somewhere in the neighborhood of 75 yards.

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Some say yes others say that they should not . Shotgun barrels are made so that the barrels tubes come together at the muzzles . Centers at the breech varied so the convergence was never a real consideration .
You can work it out mathematically by taking the centers at muzzle away from the centers at breech and dividing that by the length of the barrel to give the taper .This can the be projected to find the cross over point . In my experience experimenting with lasers at 30 yard the right barrel will shoot to left of center and the left to right of center . To make a pair of shotgun barrels that have over lapping patterns at 30 yards the barrels at the muzzle would have to be spaced about 5/16"to 3/8 "on a 28 inch gun dependent on the center at breech .

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Originally Posted By: Vol423
If an exceptional gunmaker were to produce his most perfect set of barrels, what would the convergence pattern be at various distances?

If he were "exceptional", he would ask what you were going to do with the gun, and at what distance you wanted to have them hit. IMO.

Originally Posted By: Vol423
Would the barrels shoot closer together until they reach their convergence distance, then cross and spread apart at longer range?

Yes.

Originally Posted By: Vol423
What would that ideal picture be at 10, 20, 30 40 50 and 60 yards?

That depends on what the customer wanted. Most of us get what we get, which is whatever the gunmake decides and whatever his effort results in. I think the commonly accepted goal is 40 yds.

Originally Posted By: Vol423
What is the optimum convergence distance for a 12 gauge upland gun?

Some of that depends on whether you hunt a flushing dog or pointing dog or just walk up birds. My preference for an upland gun would still be the common 40 yds...because, as Bill pointed out, who can tell an inch or two on the pattern board...and it becomes more important as distance increases that your POA is close to your POI.



As Birdman stated, a shotgun moves left and right when the gun is fired. As the gun moves, the shot is traveling down the barrel. Where the barrel is pointed when the shot leaves the barrel is what determines where it will hit. That's why a common .011 convergence would have the static (gun at rest) crossing point of the barrels at about 9 ft, but that obviously isn't where they hit when fired.

Last edited by Chuck H; 05/04/13 01:11 PM.
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