Big Barrels Yet Again


Bruce

I’ve been reading your “Technoidisms” and a thought occurred concerning big bores (.780 or .800).

What effect does a “big bbl.” have on:

#1.shotstring,
#2 velocity,
#3 choke constriction correlation ie. .40 = full choke etc. etc.
#4 patterns.( less friction = less deformation = denser patterns?)

One of the claims by the makers (Moneymaker & Baker) is increased velocity over “standard” bbl’s. so if your theory of 1200fps being about the max. “useful” velocity in a standard bbl., does this hold true with the fat bbl’s.? Should I perhaps shoot 2 3/4 d. loads instead of the 3d. loads I’ve been shooting?

Obviously the felt recoil is less based on my personal experience, is that the only benefit?

Thanks again for your expertise, I’ve fwd’d. your stuff to my trapshooting buddies and most appreciate your detailed approach to shotgunning.

Dick

Dear Dick,

When I first started fooling with overbore barrels, porting and long cones, I thought that it was all smoke and mirrors. After all, the only way that a machine shop makes money is to put metal shavings on the floor. Any excuse to do that pays the rent. Now I’m not so sure- a most typical state of mind for me.

Stan Baker advertises that his “Baker Big Bore” with an .800″ bore (basically a 30″ 12 gauge chamber) adds about 50 fps to a given load because it reduces friction and provides a broader base for the gas to push against. I borrowed a Perazzi MX-8 with Baker’s barrels and shot it for a day, but I never did chronograph it with my standard loads. The gun didn’t really seem any softer recoiling to me and it sure did sound funny. It seemed to “boom” instead of “bang”. I never got any real gas blowby that I could detect, but I didn’t shoot on a really cold day either. If you use anything except a premium wad and shoot on a cold day, I’ll bet you do get blowby. It sure happened on a friend’s B25 that he had someone cut “extra long” forcing cones on. If it can happen in just the forcing cone area, it can certainly happen when the entire bore is hogged out. Bakers .800″ barrel is still being sold, but it hasn’t exactly set the world on fire.

Effect on shotstring? I dunno, but consider for a moment that enlarging the bore from the nominal factory standard of .729″ to .800 is an increase in bore area of slightly over 20%. This means a shorter shot column and that means less shot distortion. Less shot distortion means fewer fliers and a shorter shot string. Has to be, gotta be. That’s why the Olympic shotgunners ALL stick to 12 gauge guns to shoot their 24 gram (7/8 oz) ISU loads. Obviously a 20 gauge would also handle the 7/8 oz load, but not as efficiently. The bigger bore of the 12 is what makes the difference.

The same reasoning which provides shorter shotstring should also provide slightly better patterns by the reduction of flyers. I want to emphasize that bore diameter is only one of many factors which affect pattern, but I would think that the larger the bore, the less the distortion of shot and thus the tighter the patterns. Of course, if you are shooting skeet a 20 yards, that may not be what you want at all. It all depends on your game.

As to chokes, I think that the best way to look at it is based on the percentage of constriction which a given choke provides. Using your .040″ (normally considered an Extra Full and expected to produce at least 75% or higher), in a .729″ barrel that .040″ choke amounts to 10.67% bore constriction. In an .800″ barrel, the same .040″ would amount to a lesser 9.75% constriction. In theory, and based on choke constriction alone, the .729″ barrel with the .040″ choke should throw a tighter pattern. Of course, in the real world that may well not be the case because the .800″ barrel puts less pressure on the shot due to a shorter shot string and less setback, which might also result in a shorter shotstring.

So far this is all “angels on the head of a pin” type stuff. The ONLY way to know what you are actually getting is to go out and test it. The trouble with most tests is that they are two dimensional. Very few people have the facilities to accurately measure the third dimension or shot string. Until that type of equipment becomes more common, many people are going to take machine shop claims at their word. Other people are going to leave their guns alone and save their money.

I’ve said this before, but it bears repeating- Krieghoff sort of pioneered the backbored barrels in modern clay target shooting. Their early M32s and the current K-80s have overbore barrels of around .735″. They also have long forcing cones. The guns have excellent reputations among clay target shooters. BUT, upstairs in the Krieghoff plant where they make the super-premium Krieghoff sidelock “Ulm” pigeon guns, the bores are kept quite tight and the cones short. No one wants a tighter second barrel than a pigeon shooter. The inexpensive (but excellent) Japanese Brownings trumpet the advantages of their .740″ enlarged bores. The premium Belgian Brownings have tight bores.

Now that the porting craze seems to be on its way out (proof positive is that the ISU is now about to accept porting as legal in Olympic trap- they are always on the trailing edge of technology), the gunmakers are looking to other things that they can do to the guns. If you feel that recoil is significantly reduced by a “fat” bore, then that alone is reason enough to get the work done. As long as your wad skirt can obturate to provide an adequate gas seal, I don’t see any way that your patterns can be hurt and they may improve.

Does it sound as though I am not convinced? I do try to keep my mind open. I have shot a bunch of .735″ and .740″ Beretta 390 gas guns and really haven’t been able to notice any recoil reduction. But I did notice a recoil reduction in a backbored/ported/coned Ballistics barrel I switched on and off my 303. It was a direct comparison to my standard factory barrel and the Ballistics barrel definitely, positively had slightly less recoil. Unfortunately, all the barrel work had lightened the Ballistics barrel up so much that it was whippy and no one, including its owner, could shoot it as well as the factory barrel. Live and learn. Recoil isn’t everything.

I know that I haven’t really answered you questions with any hard facts. That’s because I don’t really have any. Nor have I seen any. If it helps, personally I don’t backbore my barrels unless I want to reduce barrel weight. I don’t use porting on any of my guns. I do run out forcing cones on some guns. Every weekend in matches, I get beaten all hollow by both people with stock guns and people with heavily modified ones. Either way, I end up losing to people who are just plain better shots than I am, regardless of the gun. If I felt that I could find a magic gun, trust me- I’d use it.

Best regards,

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

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