All --
Well, after speaking with both Eyster Heritage Gunsmiths
6441 Bishop Rd.
Centerburg, OH 43011
Ph: (740) 625-6131 ( Corrected address and phone number)
and with Briley Manufacturing -- I now have some understanding as to the degree of correction that can be achieved by these gunsmithing groups in improving the barrel regulation of a double gun -- at least in the limit of screw-in chokes. I was very much impressed with the seeming competency of both groups. Their replies to my questions were very much self-similar.
Both companies modify the the chokes for the respective barrels to achieve the movement of the point of impact for the patterns in the regulation process.
Both companies quoted similar metrics with respect to what can be achieved. The point of impact for a barrel can be moved, perhaps, 6 -- to an absolute maximum of 8 inches -- at the standard 40 yard distance. Tighter chokes can be "moved" greater distances and more reliably at the 6 to 8 inch extremes. Open chokes present more of a problem and this extreme movement may not be achievable. Pattern distortion increases with increasing point of impact movement. This distortion is small and probably unimportant, if the movement is only 2 to 3 inches. Obviously, the screw-in chokes must be used only in the barrel for which they were regulated.
If greater point of impact movement is need, the barrels may be separated and rejoined, properly. In the limit of barrels joined by brazing -- new barrels is the pragmatic solution. If the barrels are joined with "soft", tin-lead, solder, rejoining may be pragmatic. But, the joining with "soft" solders is more subject to fatigue cracking with extensive use.
Jim Eyster did make the point -- that in his experience -- the determination of the point of impact is somewhat sensitive to "who is shooting the gun" and the load being used. For geometric and recoil movement reasons he suggested that SXS barrel regulation was more difficult than O/U regulation for the manufacturers.
It appears that many, if not most, companies, manufacturing double guns, do have problems with barrel regulation -- at least occasionally .... and some more that others. I found some of the barrel regulation "war stories" [b]absolutely appalling in these discussions. I am still incredulous. But, the better manufacturers, that value their reputations, appear to quickly rectify apparent problems.
Browning appears to be the only manufacturer, which at present, is publishing and guaranteeing specifications for barrel regulation. Browning's specification is for a maximum divergence of 3 inches for either barrel from the point of aim. In the worst case -- if the tolerances for the two barrels added -- the divergence in the point of impact between barrels could be as much as 6 inches. As I understand it, typical Browning results are significantly less / better, however. In my view Browning deserves some credit on this basis.
I find this all very interesting. It is absolutely clear that the barrel regulation of double guns cannot be taken for granted -- no matter who the manufacturers is. Please read the last sentence, again.
Buyer beware!
Best Regards,
Don
