doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com What ammunition is a .725 bore 12 designed for?

Ted you think the barrels have been sleeved ?

Bit of a thought puzzle for me also, Ted. In fact, I think I've asked the same question regarding specific intended fodder for "tight" bores in European 12s (Merkel and Manufrance as examples) and got the usual advice of "pattern to find out what looks good on paper". Maybe 4 thou under nominal isn't that big a deal but you do begin to wonder at .719". I think it's beyond doubt that there's a difference of "fit" of a plastic wad in bores of different diameter and a corresponding difference in produced pressure due to friction and assured complete obturational gas seal in the tighter bores. I have had stuck wads a few times and carry a wad knocker (5" long chunk of brass bar stock)which will remove a wad obstruction on a typical overbore (.740 or so) target gun. It wouldn't budge one in the bore of an old .723" bored Beretta and I had to resort to the range rod. I've never stuck a wad in a 12 ga. Moneymaker barrel bored .789".

Back from the anecdotal to the question at hand, I also would like to know if there is "intention" in boring tight and an optimum design load in terms of components for such guns. Bore leading aside, if I knew the intended fiber wad load for my Merkel 200 (problem also compounded by choking differential in one barrel of over .050" below bore diameter), that's what I would be loading for work involving flying things other than the bitumen sort. CIP pressure limits I understand. The thinking (or lack thereof)by which these guns got "grandfathered" into the plastic wad and shotcup era I don't understand.

jack

I would use the wad you feel gives the best pattern. I seriously doubt there's a line that can be drawn in the sand on this one.

I'm a pragmatic kind of guy. The European bores are designated to the nearest tenth of a millimeter. which is to say they are measuring to the nearest four thousanths. Some might think that's a little sloppy and if a bore turns out a lttle on the tight side, hey, look, it still measures 18.4 mm, so all's good.

I checked. My Perazzi is 18.4 mm (their measurement) and my two Belgian Brownings are 0.725-0.726 in (my measurement). The oldest of the Brownings is a '66, so it's anyone's guess as to whether or not they gave any consideration to wad types.

I have been measuring a lot of shotgun bores lately, most relatively modern imports. I have yet to find one with anything close to .729. Most are high teens to .725. Everything else is all over the board. Old English 10 that is spot on .775(which seems kinda rare)...old NIG from same timeish at .750 and .760..wich seems way outta line. Most american doubles spanning between just before both wars seem to be .720-.725.

Best,
Mark

The limits of precision of tenths of a mm relative to that of thousandths of an " didn't occur to me. I am schooled. As soon as someone explains the salutary advantage of choking .054" under bore diameter (I'm talking bore dia. of .719-.720" in a Merkel)I will stop scratching my head about that also.

jack

The biggest bore in the Perazzi pile here is .727 and the majority are .725/6. They have tens of thousands of rounds thru them and seem to work just fine.

I think the elephant in the room here is that your question sounds like something phidoux or WTF would ask. I mean, are you kidding?

Dr.WtS

Thanks for the sanity Wonko.

Researcher,

I'm curious about those 1880's-1890's Parkers with .750" to .757" bores. Are there any factory specs or data from that time to suggest that those bores were within original tolerances? My usual knee-jerk reaction when I hear about 12 gauges with bores that large is that they may have been honed out sometimes in the last century or so. I could be wrong, but I think the Parker cult following that has existed for so long may have led to a higher percentage of them being shined up. Have you encountered smaller bores in the same vintage Parkers? Thanks.

FWIW, typical older Beretta bbls are .721~.724.

Seem to recall some conversations here and read in some treatise as well stating that Italian proof house rules limited the nominal bore dia. to near what we would call normal, i.e., .729 & were out of proof at .730. That thread discussion took place a long while back.

Keith - no proof, but my impression is that those large bores were the result of someone taking out pits and rust. They seem to be uniquely associated with guns that lived in the blackpowder era. By whatever means, I've never encountered a big bore, say over 0.740", that showed any sign of less than factory or professional work.