Barrel Convergence Woes


Bruce,

After swearing that I’d never shoot a O/U guess what I bought…a Browning 325 with 32″ barrels. I’m hoping it could become the basis of a project gun. I’d like to put one of Bruce Ney’s shock absorbing stocks on it and lengthen the cones (punching up to Master class has me looking for all the “shooting edges” I can find, and I know how many times I’ve wished that I had two chokes for those long/short presentations…probably self-defeating but hey, why not!)

Anyways, here’s the problem! After learning the hard way that you must always pattern guns to find out where they shoot I patterned this gun my very first time out with it. I shot .030 chokes at 20 yards to see where it’s hitting. The bottom barrel was just an inch or two high probably equating to 65/35. The top barrel was quite a bit high, Maybe 4-5″. After opening up the choke it was probably 85/15.

The interesting part is that I patterned with some 3 dram 1-1/8oz reloads. When I tried a few 7/8 oz. loads the point of impact dropped with the top barrel. It seems to me that I’ve read somewhere in your archives that longer barrels tend to shoot higher due to recoil having more time to push them up. I could probably live with this if both barrels shot equally high, although I’ve got my face pushed down on the stock to the point where I can’t see the rib, just the beads, so there’s probably not much help in dropping the stock down.

The real problem is adjusting my point of aim for two different barrels. While practicing, when I mentally adjusted my aim point for the upper barrel (probably almost a foot under the bird at 40 yds) I was crushing them. I then had to change the aim point for the bottom barrel (pretty much right at the bird or a bit under) Please help!!!

By the way, the Browning Gold I shoot now patterns 50/50. This experiment was designed to make things easier for me in the shooting box, not create two different aim points. Do you think one of those “coil-stocks” would absorb (slow) enough recoil to bring the aim point down or do I just shoot 7/8 oz. 7-1/2’s at those 45 yd crossers severely handicapping myself. Or just scrap the whole idea (least fun option). Thanks for your input!

Steve

Dear Steve,

One of the reasons that I shoot gas guns in competition is that barrel convergence on an O/U drives me crazy. I remember having a Browning B25 Superlight 12 gauge grouse gun. I was deadly with that thing. I was particularly good on escaping “bonasus umbillus” with the top barrel and it’s modified choke. One day the Devil made me pattern the gun and I found that, with the loads I was using, that the top barrel shot a FULL pattern high at 40 yards. I never could look that gun in the eye again and sold it.

I couldn’t live for five minutes trying to compensate for one barrel that shot to one place and another that shot elsewhere. Ignorance is sometimes bliss. Maybe patterning it wasn’t such a good idea.

You are very smart to have realized that point of impact, particularly with the high off-axis top barrel, can vary quite a bit with the shell used. Most people don’t realize that. You might try fooling around with a number of different brands of target shells of standard shot load. You may find that barrel convergence is better with some than with others. The Victory 1-1/8 oz “480” 2-3/4 dram shell is noticeably softer than the STS of the same designation. I’ll bet that they would impact differently too.

If you can’t find a combination that suits you, as I see it you have two choices. You can have the barrels re-regulated- a nasty and expensive job. Or, you can get eccentric chokes from Briley. They will give you screw chokes cut on a bias that will make that top barrel of yours shoot anywhere you want it to with a given shell.

I had a Parker Repro in 28 gauge that had a left barrel which threw at least a full pattern left. Many of the Repros had barrel convergence problems. Fortunately, that barrel also had the original “gunmaker’s chokes” and had never been cut. A local gunsmith just cut in the proper choke at a bias and it worked like a charm. I was lucky to have had enough choke left there to work with. Briley can always sweat in a solid permanent choke of any diameter and cut it to any bias you want. Maybe that is what I should have done with my Superlight 20 years ago. Live and learn. You are lucky that you have screw chokes.

Barrel convergence is a problem for all gun makers. Most makers today are very proud if they can get the barrels to shoot within 6″ of each other at 40 yards with a standard shell. With screw choke guns, test for convergence with Full choke because it is easier to estimate the center of the strike. Use the same choke in each barrel to make sure that you have eliminated all the variables possible.

As to the pneumatic “coil” stocks, be careful. I have used the old Docwiller Hydracoil on a Krieghoff 32 and also the new Soft Touch and G-Square on current guns. I found that the devices worked marvelously in the mounted gun games of American-style skeet and trap. I found them far less satisfactory at the low gun games of International Skeet and Sporting Clays.

The problem is that to work correctly the “coil” stocks have to be firmly seated in the shoulder. That’s easy in the pre-mounted games, but in the low gun games a firm shoulder mount is really a rare thing. You never really tuck it in the way you should. When a coil stock isn’t tucked in tight, it really seems to recoil with about the same amount of pain, misery and face slap as a standard stock.

Also be aware that the coil stocks have heavy mechanisms and can add considerable weight to the back of your gun. Try putting six or seven ounces of lead in your buttstock to get a feel for how the gun will balance after you install a coil stock.

I have absolutely no idea how a coil stock would affect point of impact and barrel convergence. I’ve never tested that.

There. Now you know everything I know about barrel convergence. Abysmal, isn’t it.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error, never in doubt.)

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2 Responses to Barrel Convergence Woes

  1. Hassan Abouzeid says:

    Hi David.. sorry for late response, but better late than never. Don’t know about your first question so won’t attempt to tackle that, but POI of the first barrel does not depend on SxS or O/U, it depends mainly on stock measurements (drops). By adjusting the stock (or having a custom one made), you can make the gun shoot as high or as low as you like. I like shooting 90/10, so my 2 competition shotguns have stocks that make themshoot that way. As for the second barrel, it ideally should shoot where the first one does (within 3 inches at 30 yards is just fine), although some expensive shotguns (like my Beretta SO) are actually designed to shoot the lower barrel slightly higher than the upper one. This is a specialised trap gun, and trap targets tend to risely sharply initially, then even out, thus the flatter trajectory for the second (upper) barrel. I still prefer identical POIs for both barrels, my favorite Peraazi MX8 with 28 inch barrels shoots almost perfectly concentric patterns at 30 yards. Greetings from Egypt! Hassan

  2. David Dabaco says:

    Very interesting Bruce! Just a couple of follow up questions:

    1. Do you know how and at what stage of the barrel manufacturing process POI is established, checked, and/or adjusted? I suspect once each individual barrel is straightened, manufacturers simply solder barrels together using jigs and later cut the chokes without checking for POI. Is that true?

    2. As in Steve’s situation with his Browning 325, do O/Us generally pattern higher than SxSs?

    Thanks in advance,

    David

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