doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Barrel convergence, seperation questions.

The recent topic on barrel seperation in .410 SxS's got me thinking. Bear with me and I will try to phrase the questions so they make sense.

When the same size frame with same fireing pin spacing is used with different length barrel sets of the same Ga. what happens to the distance that the shot charges will converge?

Assume that you have 26", 28" and 30" barrel sets and all muzzles meet with no seperation.

It would make sense that the shorter barrel set would converge at a shorter distance than the longer set(s)due to the more acute angle of the barrels. Is this true? Does it matter much?

Chief

If you trig out the convergence per inch, it doesn't change much.

I agree, it doesn't. So the "barrels touching" is mostly aesthetic, or tradition. I've noticed that a lot of the new SxS's have a good amount of seperation between the barrels, no matter the Ga. of the gun.

Chief

As I recall from the L C Smith Plans & Specifications book their bbls converege at approximately .011" per Inch. I checked several of my Lefevers some years back & they had near identical convergence to the Smith specs.
Much harder for me to understand is how a set of 28ga & .410" bbls could both be built to the same frame, both touch at the muzzles & Both hit point of aim. The convergence would be much greater on the .410.

They can't... and they can. Small gauge barrels are very flexible.

I would suspect that the outside diameter of the .410 barrels and the outside diameter of the 28Ga. barrels are close to the same. The .410 barrel walls are unusually thick compared to other gauged barrels. That would put the centerline of the bore in nearly the same place, right?

Chief,
While my .410's have thick breach walls, they still aren't as large as a 28g at the breach. The muzzles are definitely much smaller than a 28g as well.

I think the popular assumption is that the barrels are each straight on all guns. I think you'd be surprized to find that isn't always so.

Chuck,

No surprise! I had an interesting talk with a gunsmith that was employed by a once major builder/importer of SxS shotguns. He did say that a lot of the SxS barrels are indeed slightly and intentionally bent. Anecdotal yes, that said, I do believe him.

Chief

I think that the "used to be commonly known" fact that double shotgun barrels are not soldered together straight has been misplaced by modern shotgunners. Also, "shotgun pattern convergence" is a contradiction in terms. Two barrels whose centers are, let's say .410 inches apart, do not converge at 40 yards. They both shoot a straight line to the target. Identifying a .410 inch difference in point of impact in a 40 yard pattern is beyond the capability of any human.