Caution to the reader. The following may be true/false or none of the above. Do I need to understand aeronautics to fly in an airliner? Do I need to understand automotive mechanics to drive a car?? Do I need to understand barrel regulation to shoot a gun?? Maybe not but now I want to, even as the midnight hour is swiftly approaching.
After asking questions and getting answers and thinking about it all, I'm less confused (or more) and may or may not have it straight.
SXS barrels have a straight bore
SXS barrels Outside Diameter is greater at the breech and narrower at the muzzle but the bore Inside Diameter is consistent so... the wall thickness is greater at the breech and less at the muzzle and the least midway along the barrel length.
That we can see with this diagram posted a few times on the forums.
From this diagram the breech OD is 1.205 and the muzzle OD is 0.825. OD midway is 0.799 The variance from breech to muzzle is 0.38 but midway the variance is greater, being 0.406
To have the two barrels become a single unit, Dean just explained that the breech end is filed to half its thickness and the two brazed together. The filing would have to start at half thickness and continue at an angle toward the muzzle that allows the two muzzles to just touch. That angle changes according to the length of the barrels. Now there is a lot of space between the two barrels from the brazed join at the breech and the touching barrels at the muzzle. This space is filled at intervals with soldered shims - more shims midway than at either the breech or muzzle end. Shimming has an effect on regulation as does the angle of breech wall filing, as I understand it. The gun can be fired without the rib being laid and adjustments can be made in the shimming to achieve the desired regulation. I think
As I understand it, the purpose of regulating the barrels is to have the payload from either barrel hit the same point of impact at a specified range. A waterfowler may be regulated for 40 or 50 yards and an upland gun may be regulated for 20 or 30 yards. It could be regulated to a customer's specification.
Beyond the point of regulation, the shot strings will cross each other. Before that point, the two shot strings will be converging and beyond that point, the two shot strings will be diverging.
Given that the diameter of an effective pattern is approx 30 inches, a bird in the center of the point of regulation is quite dead. Moving the bird further down range and not moving the barrels, the bird will be closer to the edge of the pattern until it is eventually not in the pattern. Same effect moving the bird closer (but of course the pattern diameter is less and less so if you connect you have a dead bird but nothing left to eat
).
I'm still unsure how shortening the barrels, with the shims not having been touched, changes the regulation. I can see that the choke may be changed, thus opening the pattern earlier and reducing effective range. For example, a heavy waterfowler is now a short range upland gun. This part remains unclear to me.
I may or may not see Dean's point regarding shortened barrel causing a shooter to hit high. Now if one were used to a 32" gun (uncut) would this shooter hit high with a 28" gun (uncut) ???
I know when I close my eyes and pull the trigger, sometimes I'm high, sometimes I'm low, sometimes there's a dead rooster sometimes there's not. I guess I need to concentrate on seeing just the bead and bird, but when I try that, the bird inevitably carries on untouched. But I am glad the Parker Bros got it all figured out for me, even if I don't quite understand it all yet.
Cheers,
Jack
Here are some images of a barrel set with ribs removed showing the soldered shims. Sent my way from Jent to help explain some of this.
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