I have a Beretta 686 Onyx Sporting model with 30″ barrels. After noticing a trend of low shot placement, I tested for “point of impact” using the method you have described in Shotgun Report. (five or six shots while mounting from different angles at 30 yards using the same full choke tube for both barrels).
I found the bottom barrel centers its pattern a full six inches low at 30 yards and the top barrel is on or only one inch high. I called Beretta Repair and they told me this difference was considerable and told me to send the gun in. They shot my gun and found the bottom barrel centered 6 1/4 inches below the top barrel. They returned the un-repaired gun saying “this is within our specifications.”
I called them back to find out what their specifications are. Their specifications are for barrels to shoot within 20 cm (7.88 in.) of each other at 30 meters. I was upset about how Beretta handled the situation and have discussed my claim with their Repair Dept. Mgr. He said their patterns (6 1/4″ difference) were “not even close to the specified tolerance of Beretta.”
What option would you advise? Live with the difference; sell the gun and buy a new one; let Briley rethread and choke the bottom barrel; stick to autoloaders; or any other ideas.
One of the reasons that I always try to buy used guns, rather than new ones is that I can test the point of impact before committing myself. The very design of the O/U “wants” to throw the top barrel higher than the bottom. The makers are well aware of this. Some go to greater lengths to correct this than others. Careful testing and mating of the barrels can easily solve the problem during production, but once those barrels are siamesed and the ribs soldered in place, realignment becomes more difficult.
How bad is a 6″ difference at 30 yards? Well, I dunno. It really depends more on you. I once had a jewel of a solid rib Belgian Browning Superlight. I killed a whole bunch of birds with that gun over many years. I shot that gun better than any I owned. I was particularly good with its second barrel. One day the devil made me test its point of impact. At 40 yards the top barrel was one full pattern high! Aarrgghh! The combined patterns looked like a figure “8”. Aarrgghh! again. I sold it in a heartbeat and bought another B-25 Superlight with proper convergence (which I don’t shoot as well). Possible moral: if you shoot a particular gun well, don’t tempt fate by testing it.
Once I had a Perazzi Comp 1 trench O/U. We had two full Olympic trenches in the area at the time and I doted on them. I was sudden death with the under barrel, but just couldn’t hit anything with my second barrel. You guessed it- it shot high- real high. I should have tested point of impact before I bought it. Live and learn. Dumb ‘n dumber.
Point of impact problems aren’t relegated just to O/Us either. I had a gorgeous little Parker 28 gauge Repro with two barrels. I bought it new, so I had to take what I could get. The short, ic/mod open barrels were dead on. The long mod/full barrels were off. The left, full barrel threw its pattern 1/2 pattern left. Fortunately, Parker Repro had never even bothered to cut the gunmaker’s choke on that left barrel. It was still chromed and had .042″ in it. I sent it back to Parker Repro and they were able to cut the choke on a bias to center the pattern and still keep it nice and tight. If the choke had been properly cut in the first place, there wouldn’t have been enough metal left to do that and still keep a tight choke.
Belgian Browning, Perazzi and Parker Repro- quality makers seem to be just as susceptible to misaligned barrels as the more modestly priced guys. Beretta’s standard of 7.88″ at 30 meters is shameful. That would approach 10″ at 40 yards. If you use Warren Johnson’s most excellent “Choke Chooser” pattern analyzer you will note that a maximum legal load of #7-1/2s on an edge-on target at 40 yards has AT BEST a 12″ killing pattern. Do you really want to give up 10″ of your 12″ pattern? I don’t think so, Pietro.
What do to? I would not own a target gun that did not have virtually perfectly combined points of impact. I am a bad enough shot as it is and don’t need any extra grief from the gun. Briley CAN cut you eccentric screw chokes to correct this, but I would never have faith that they would line up perfectly every single time. Perhaps they do, but it would always be in the back of my mind. Every time you had to put the special choke in, you would be reminded that your gun wasn’t quite right. Those chokes aren’t cheap either.
I don’t know about re-threading. That might be an option, but the problem is probably in the alignment of the barrels themselves, not in the threading. The new threads would have to be put in at an angle and your gun may not have enough extra steel in the barrels to accommodate this.
Personally, I would sell the gun to one of your closest competitors. A good candidate would be the last guy to beat you in a shoot-off.
Whether you buy another O/U or an auto is up to you. I shoot clay targets with both O/Us and gas guns, but perform best and most consistently with the gas guns. It is easier to adjust the fit of a gas gun, the barrel point of impact is never a problem and the reduced recoil makes them easier to shoot well. The O/Us do have some advantages, but their shortcomings are more important to me. If you do get another O/U, I’ll bet that you test the point of impact of both barrels before signing that check.
Shotgun Report’s Technoid
(Often in error, never in doubt.)