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

From page 61:

"When the barrels were taken from inventory for fitting to the frame, the barrel flats were then milled in and the breech end cut off to the appropriate gauge. Extractor holes, chambers, and shell cuts were then drilled. At this point the barrels were made for either a raised matted rib or ventilated rib. Once the rib was in place the barrels were fitted to the frame and proofed. The gun was then taken, still in the white, to the 40 yard range and fired to determine the point of impact. Model 21s made prior to 1960 were designed to shoot slightly low of dead center. Both barrels were expected to impact the point of aim at the same place."

Mike

Gentlemen --

We seem to be accumulating a significant amount of information in this thread that indicates that barrel regulation is poorly controlled within the industry.

I may be / have been ... naive -- but, I find this result surprising -- if somewhat disconcerting. I expect you do, as well.

The relatively close superposition of the point of impact for both barrels is inextricably tied to the basic concept of a double gun. Clearly, the double gun has many design advantages from esthetics ... to safety -- from dual chokes... to light weight. But, if the double gun does not shoot where you point it -- all these advantages fade into irrelevancy.

What is going on here? It seems that the point made by several of the contributors -- that the shotgun manufacturers expect that most people will not critically pattern their guns -- may indeed be correct. They expect to simply "slip by". It also occurs to me that the gun manufacturers never define / guarantee the tolerances associated with barrel regulation. In this context the reasoning is clear. Disappointing! Perhaps, we as a group, are too 'accepting" of this shortcoming. Perhaps we can actually shoot better than we think we do! Think about it! There may be an "opportunity" for a double gun manufacturer, which "bites the bullet" and guarantees a set of minimum barrel regulation metrics that insure quality.

I cannot believe that the regulation of the barrels of a double gun is impossible to consistently control in the context of manufacturing. It is clearly a matter of identifying the critical manufacturing variables and controlling them without fail. The question of barrel regulation should be integral to design of the double gun manufacturing processes and quality control protocols. Having a double gun that shoots where it is pointed should not be an "accident".

We should refuse to accept guns with poorly regulated barrels. Frankly, I am disappointed in how long it took me to critically evaluate the patterning of the B. Rizzini shotgun that started this thread. But, you have my assurances that it will not happen, again.

Best Regards,

Don

I purchased a Fabarms Sporting Target Model, O/U, then imported by HK. The gun patterned top barrel 55/45 above center the bottom barrel 20/80 per their factory tests and they said it was within factory spec's. This is a target gun. At a local shooting fair I met the HK rep and told him I was prepared to
1. sue HK in small calims court for selling a target gun which failed to be satisfactory for it's intended purpose, 2. To wear a sandwich board at future fairs and exhibits with the pattening sheets attached to draw attention to the lack of convergence.

The rep being of a cooler head than mine asked what I wanted and I said a Briley choke job for one barrel or replacement. He called back the next day and told me to again send the gun back to HK and the sent back a new gun. Does the new gun suffer from nonconvergence? Yes but not as bad as the first. I have to shoot the bottom barrel for the 2nd or fall away bird on trap doubles and hence reverse the order of shooting. Open barrel on top, tight barrel on the bottom.

Now we know why double rifles cost so much more than shotguns,you got to get the booggers out with rifles.

I have read that part of getting double rifles to shoot to the same point is the right load. The right bullet at the right velocity.

Changing the cartridge velocity or shot mass in a shotgun changes the point of impact. I can't imagine the changes could make up the differences in POIs posted here by Bill Henderson and by mike cross however.

Best,

Mike

While I agree that "production" gun manufacturers do not provide absolute control on POI/convergence/etc., I think they do/did a fair job considering they never shot most of the guns at a board. Their downfall may be that some makers don't stand behind their product to the satisfaction of the customer.

My first BSS patterned with one barrel off a few inches (it's been 20 yrs since I patterned it) but I still found it acceptable to me.

To illustrate the precision or lack of precision required for achieving acceptable POI of both barrels, I can share my experience with the recent strip and re-laying of ribs on my Parker. I desoldered the ribs and the muzzles, cleaned between the barrels and all ribs, then wired them together with the muzzles touching as before, then leveled the barrels with the method shown in the picture. The barrels shoot nicely on top of eachother. I need to do more patterning to tell you by how much they misalign, but I did enough to see they obviously are well under what I consider maximum.

Did you pattern it before you relayed the ribs ?

This is just my view, but I am first interested in point of aim performance....that is, when properly fitted and mounted in a repeatable stance, does the gun hit where I point.

If there is a problem showing when patterning off-hand, then I believe you need to sand bag the gun on a stable platform and pattern it like you were sighting in a rifle....this will provide definite proof if you have a point of impact issue, and in particular a difference in point of impact between the two barrels.

I'm sure there are many more expert at this than I...just wanted to share my thoughts.

Cheers

Baron I agree. If the barrels both shoot to the same point the stockers can fix the gun to shoot where I look.

Best,

Mike

Mike --

I found the Winchester Model 21, barrel finishing, discussion you posted interesting. But, in your posting the Winchester discussion of barrel regulation was solely focused on the height of the point of impact for both barrels with respect to the siting plane. The bending process is clearly a way of controlling the height of the point of impact -- at least on SXS designs. The bending process affects both barrels in roughly the same way in moving the respective patterns up or down. O/U designs may not be amenable to this approach with respect to point of impact height, based on structural considerations related to stacked barrels.

But, in the posted outline on barrel regulation there was no reference to barrel regulation procedures related to superimposing the point of impact of both barrels on the same point at 40 yards. Here, I am referring to the barrel to barrel pattern regulation. Was there any discussion of this point in the Winchester reference?

Thanks.

Best Regards,

Don