doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com What is the ideal convergance of SXS barrels?

The barrels on a Darne slug gun are regulated to 55 yards. I found it interesting that the customer who ordered the single one I sold was asked to specify what chokes he wanted (Darne slug guns are considerd true dual purpose guns) and after the chokes were cut, the gun was regulated.
The gun was equipped with a folding leaf rear sight, and a partridge bead on a ramp in the front. When fired with Federal slugs (it had been regulated with Federal slugs, in France, if I recall correctly) the black center of the target had two holes that looked like a pair of eyes looking back at you. It handled fine birdshot very well out to about 35-40 yards.
Yes, the barrels had to converge to do that at 55yards. At longer ranges, the slugs would have eventually crossed paths
Wes Gilpin owned a similar Darne slug gun that was a much higher grade. He used his for sea ducks, and had a detachable claw mount scope mount made up here it the states to mount a 4X scope. He used the gun setup in this fashion to take deer and pigs. After Wes died, his gun came to live in Minnesota, and the owner made contact with me, but we haven't had a chance to get together with the gun.
I assumed that regulating a slug gun would be about like regulating a double rifle, but, the maker told me it was pretty easy in comparison. I took him at his word on it.

Best,
Ted

Amarillo Mike and I are the only posters on this thread that seem to realize that a pattern .9" to the left or right of center to infinity is as good or better than a pair of patterns that converge at only one range and then divert in opposite directions. My vote is that the "infinity" pattern is better.

Reality often gets in the way of theory, even good theory...

Best,
Ted

Most of differences expressed here are semantic. You don't get common points of impact with a side by side shot with typical gun mount -- out to infinity or otherwise -- without barrel convergence.

"Theoretically" ... if the load is perfect for the gun's barrel convergence, the barrels are perfectly parallel to the "line of aim" when the shot leaves the muzzle, and the pattern centers are delivered to virtually the same point at all distances, without crossing. Patterns shot with a lighter load cross at some distance; with a heavier load, the pattern centers never coincide, and divergence increases with distance.

As noted before, lots of factors can muddy actual results. The above assumes consistent velocity. It also seems to me that even cast could affect how much each barrel of a side by side moves before the shot exits the muzzles.

Jay

I wonder how the center line of the bores of a side by side shotgun be set to ensure that the patterns of both barrels fly parallel to each other.

Quite simple to make from new , but would look ugly and rather like a big bore double rifle .You will also need extra wide ribs that will add to the weight . I feel a point some seem to have missed is that with a shot gun you shoot a spread of shot where you hope your bird is, you are not aiming at a sitting target so it is a matter of learning where you gun shoots and giving lead accordingly .

A quick calculation suggests that the muzzles are about 1 1/2" apart, or 3/4" to each side from the aiming line when the shot leaves the muzzle

Chuck for centerlines you get 1/2 of each muzzle diameter plus both of the wall thicknesses of the barrels at the muzzle.

So (1/2 x .729) + (1/2 x .729) + (2 x .040) = .809"

Your calculation was too quick

Mike,
I think you've been inhalin' too much Britanny poo air. I did say "...when the shot leaves the muzzle". In order for an .011" convergence barrel set to get a barrel pointed at the target, it has to move laterally. That movement only has to be about 3/10ths of an inch if it pivots from the butt of a 50" long gun. 3/10ths plus half your .8-- is about 3/4" or thereabouts, apart from the centerline (aiming line), or 1 1/2" apart from the other barrel when that barrel is fired and the shot leaves its muzzle.

Mike is right, Chuck is covering for his bad arithmetic. The truth is that double shotgun barrels are not straight, they are somewhat bent when being soldered into place. Parallel patterns are created by bent barrels. The Brits figured that out decades or centuries ago. Do you fellows really think that tubes that are a defined distance apart at the breech and touch at the muzzles all shoot exactly converging patterns without bending? They are bent.