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

Don in response to your question about acceptable "Point of Aim versus Point of Impact" I have done some research and found very few definitive answers. I have a Beretta SO5 which is a hand made over and under. At 40 yards the bottom barrel shoots 4" lower and 6" to the left. I used a pattern analysis program called "Shotgun Insight" to analyze the data. This bore out over several different cartridges and chokes. The patterns were shot freehand. Over on 16gauge.com the resident BBS know-it-all stated he got a figure from Browning of no more than 4" difference in point of impact between the two barrels. He quotes Stan Baker all the time and says Stan helped him get satisfaction from Browning.

Best,

Mike

Don,
Have you identified if the barrel bore of the top barrel is off or if it was just a misaligned machined screw choke bore and thread? 16" @ 40 yds should be discernable by blocking up the barrels and sighting the bores vs. the other barrel and the sight picture.

Mike --

Thanks for the information, re: your SO5, Browning and Baker. This "4 inch, maximum differential," metric seems consistent with some information I remember reading, years ago. (I cannot remember where.) Its seems that this was considered a reasonable manufacturing tolerance for double guns. But, if you do the arithmetic, assuming straight barrels, this 4 inch point of impact tolerance implies an 0.078 inch difference in spacing of the bore axes - front to back - along the length of 28 inch long barrels. That is a very large value for a manufacturing tolerance for this dimension. Perhaps the assumption of straight barrels is a poor one. Additionally, there is the question of the axial accuracy of threading of the barrels for the chokes. It all adds up. Interesting -- if disconcerting.

Best Regards,

Don

Chuck --

I believe your point about fixing the barrels in position and sighting through the barrels at a distant mark to assess the alignment of the barrels is correct and a good suggestion. A mark centered in the view presented in one barrel should also appear centered in the other barrel -- with correct / parallel barrel alignment. But, as you probably know, one must have the eye precisely located along the axes of the bores in making this evaluation. When aligned with the axis of a straight barrel the eye sees a set of concentric rings. Concentric rings will not be found, if the barrel is not straight. Some ring distortions will be found in this case.

I undertook this procedure, when I purchased the gun and the result looked reasonably good. I could not ascertain any significant difficulties / misalignment. Even the ring concentricity appeared reasonably good.

As impied in your note, all together -- these findings may indicate that the threading for the chokes is at fault. But, the choke threading appears to be centered in the bore of the barrels at the muzzle. The wall thickness appears to be uniform around each barrels periphery. But, I can more carefully measure these wall thicknesses as you suggest. If the threading for the chokes, alone, was the cause of the differential impact and if the difference was ascribed to the threading of one barrel, choke threading would have to be "off by approximately 0.021 inches to explain the result. That is a lot of choke misalignment. Perhaps both chokes are "off" -- but opposed directions in the same plane.

Of course all the tolerances add up ... each barrel's straighness, brazing alignment, choke threading, etc. It would take some very careful measurements to "sort this all out". I am not equipped to make these measurements. And, right now, I am a little discouraged by the situation. But, in the end I will have a grouse gun that "shoots straight"..... "come hell or high water"..... Rizzini notwithstanding.

Thanks again.

Best Regards,

Don

I have seen a few guns with 'crooked' barrels in the past. I actually owed a 3200 with the top barrel that was curved so bad you can see it very easily just by looking down the top of the barrels as if sighting. The rib was factory brazed, secure and straight, while the barrel swooped out to the side then back in. All indications were it was built that way. The lower barrel was straight. I also saw a 101 with similar problems, as well as a Grulla sxs that barrels that curved upward quite a bit. The Grulla may have been altered or built that way, I couldn't tell.

Hopefully, someone like Eyster can remedy the problem or Rizzini can be convinced they built a clunker that they don't want out there tainting their name.

I had a problem with a Grulla this year that shot 6" low @ 16 yards. I sent it back to Merkel and they contacted Grulla who then said that it was within Tolerances. Danny at Merekel agreed with me that this was crap and replaced it for me. But I think it goes to show that eventhough a 4" spread is what a tolerance should be some mfg take a more liberal stance.


P.S. I was talking to the FAMARS representative about why they would use mono-bloc construction on their fine guns and he said that barrel regulation is more difficult with chopper lump construction than with mono-bloc construction. I know this might not set well with the tradtional crowd on this board and I believe that your Rizzini is a Mono-bloc as well, But I think it is insightful.

Years back I was head set on setting up and over/under to turkey hunt with...after going through three Browning's a Beretta one American arms and one Fabarm I finally gave up...the bottom barrel on all of them patterned from 6 to 9 inches low at 25 yards progressively worse at longer ranges.

The only manufacturer I contacted was Beretta they said 9 inches low was within their specs. I think what they are banking on is the average guy will never check point of impact on a shotgun.

I believe there are two different regulation issues. First issue would be how close the barrels shot to the same point. When I mentioned 4" that was supposed to be the maximum difference between the POI (point of impact) of the two different barrels with the hold point being the same.

The second issue would be where the gun shoots for the individual. I guess IM's low shooting Grulla could have been placing both barrels within 4" of each other. Maybe it was regulated for someone whose cheekbones were at the corners of their mouth.

Barrel flipup was mentioned in a previous post. In the Winchester Model 21 book the author memntions after some years after it's introduction Winchester started flipping the barrels up to make 21s shoot higher. Looks like they could have just stocked them higher!

Best,

Mike

Best,

Mike

Mike,
When you say "...flipping the barrels up..." do you mean bending?

I have straightened a set of sxs barrels that had been bent from damage. I can tell you bending a set of sxs barrels up or down is childsplay in terms of actually making the bend. The one Grulla I saw that shot very high had curved upward barrels, visually the barrels were curved. Had I known how to fix the condition then, I'd have bought that gun cheap on the spot. It was a nice 28ga.

Hi Chuck:

This is from page 65 of Winchester's Finest, The Model 21 by Ned Schwing:

"After 1960 the point of impact was changed so the gun would shoot dead center. This meant that the barrels on post 1960 Model 21s were bent slightly upward to accomplish this new point of impact. The barrel finishers referred this process as putting "up" the barrels. If one looks down the the barrel of a Model 21 made through 1959 the barrels will be relatively straight. On guns made from 1960 on, the barrels will have a noticeable bend in them. The result is not unlike the shape of a banana, albeit not as pronounced. Nick colomonico, long time Wichester barrel maker, once spent a month adjusting the barrels on a Model 21 built for baseball star Ted Williams, so they would shoot to the owner's satisfaction. Model 21s fitted with ventilated ribs were much easier to regulate because of the additional height of the rib."

Although not related to your question I thought this paragraph was interesting. From page 64:

"After the barrels were browned they were fittted to the frame and again taken to be fired on the 40 yard range. If the gun did not shoot correctly the barrel finished had several options. The front sight could be lowered slightly to make the gun shoot higher, or if the gun shot too high the barrels could be put on a straghtening jack and forced down to give the proper point of impact. If this failed the barrels would be taken apart and the entire process repeated until the gun shot correctly. This was not much of a problem prior to 1960 because the Model 21 was designed to shoot light low and the barrels were straight."

Best,

Mike