doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Problem: O/U Barrel Regulation

I have some minimal experience in regulating barrel to barrel POI from my conversion of a 20g to 28g. In my several correspondences and phonecons with Kirk Merrington, and others that have done it, they cautioned me to shoot the gun off-hand only for evaluating the POI. Their opinion was that the resistance of bench shooting the gun was different than off-hand, which could result in different POI. But, since I have never shot for POI from a bench vs. off-hand, I can't provide any direct experience there.

Chuck --

Your posting outlining your restoration work on the Parker is remarkably interesting.

The fixturing you show in the photos is substantiallty self explanatory in most respects. But, how did you control the spacing betwen the barrels? You indicated and the picture shows the barrels are in contact at the muzzle. I assume that the chopper lump provided another point at which the side to side position of the barrels were fixed. Did you use spacers along the seam betweens the barrels to eliminate bowing and to provide for barrel straightness and parallelism between the barrel bore axes?

Additionally I assume you may have used "soft", Tin-Lead, solder ( and not a brazing alloy) to join the barrels. The required fluxes for soldering to steel are often corrosive. Was there a potential problem with flux entrapment within the solder joints? How did you "handle" this potential problem?

Thanks,

Regards,

Don

Don,
I did a 'how to' thread a while back on the re-laying of ribs. Yes there are spacers between the barrels that get tinned. All tinning is done with acid flux with the parts separate from one another. Getting solder to stick without acid flux is a problem. Once the tinning is done on all the parts, a thorough cleaning to remove the residual acid flux is necessary. Soap and water with a Scotchbrite pad and small wirebrush is what I used.

This link to Drew's site that captured my thread and some of Dewey McVicker's and Oscar Gaddy's ideas is a great reference. http://www.picturetrail.com/sfx/album/view/18691676/297178486

BTW, I used 60/40 tin/lead solder. A friend that does high-end conservator/restoration type of work for a living suggested going to 63/37 true eutectic solder for the lowest melting point, but I didn't find I needed it.

Hi Don:

I probably should have edited more out but the paragraph I posted last has this sentence in it: "Both barrels were expected to impact the point of aim at the same place."

Best,

Mike

Some questions-
-I bought a 12 gauge insert that cast a laser, thinking that this would help identify POI of barrels, but I guess this would only show where the center of the chamber was pointed and have little or no influence on pattern centers?
-It seems like POI should be measured at the distance most shooting would be done? 22 yards for skeet perhaps? 35 yards for the 1st barrel at trap and maybe 50 yards for the second barrel? Games guns at...........

The lasers that fit the chamber may tell you where the chambers are pointed, but could be very far off a barrel set with regulation problems. I've even given some thought to making up a laser to fit the bores and put it in near the muzzles as possible, but the choke alignment is the last word on where the pattern hits, or at least has the last influence.

Chuck don't SxS barrels made in the traditional manner have to bend bend. That is the breech walls are substantially thicker than the muzzle walls and both touch. If the barrels didn't bend then at 40 yards the left barrel would shoot 3 feet to the right and right barrel would shoot 3 feet to the left.

Best,

Mike

Mike --

I saw the phrase, "Both barrels were expected to impact the point of aim at the same place.", but, did not know what lay behind the assertion.


I assume that the phase means that the Winchester people had a design and barrel joining process which reliabily produced the same point of impact for both barrels.

If true, it is not clear that the important elements of this joining processs are known my all members of the industry, currently.

By the way, it is over a week, now, since sending my note to B. Rizzini, inquiring as to the tolerance for the differential in the barrels' points of impact, which they could guarantee, on a new set of barrels. This inquiry resulted from their suggestion that I could purchase a new set of barrels to resolve my current patterning problem with my B. Rizzini shotgun. After sending the note, I have called the representive twice and left messages. To date, the silence is deafening.

Thanks.

Best Regards,

Don

Mike,
On the few 12g sxs guns I've taken the time to look at, the barrels were each straight, but converging. I don't recall the amount off hand now. But the number is substantial. Measuring the outside across both muzzles and then back a foot will give you an idea of the convergence. The barrels do indeed "cross point of aim", but the theory is that the recoil causes the gun to rotate and align the barrel with the point of aim (POA)as the payload exits the barrel.

I forgot to mention on page 2 that the Grulla would pattern to point of impact on the right barrel and 6" low on the left barrel. hope this clears up any questions.