Briley and Hastings advertise their chokes in sporting magazines. According to Briley, the standard bore of a Browning shotgun, not invector plus, is .725″ and the standard bore of a Winchester with winchokes is .730″ In Dunn’s catalog, they offer Briley chokes that fit, interchangeably, Winchester, Browning, Mossberg, etc., with the same item number and style for each choke. If I own a Winchester with standard bore and order such a choke for skeet, a constriction of .005.” what constriction do I get? If it is designed for a Browning invector, it should have a choke diameter of .720″, if it is designed for a Winchester, it would have a choke diameter of .725″. I could get either a skeet choke or an improved cylinder for my Winchester. For a Browning, I could get a cylinder choke were it designed for a Winchester. Why don’t choke manufacturers etch the true dimensions of the choke upon the choke? How can they sell such chokes as interchangeable?
Choke makers don’t sell chokes by the inch because the average guy doesn’t have the vaguest idea what his bores actually measure. He knows what brand of gun he has and the name designation of the choke he wants. He will almost certainly never bother to pattern test the choke once he gets it. Actually, most shooters (other than Shotgun Report readers, of course) don’t even know how a choke of a given name is supposed to pattern, so there isn’t any point in patterning. Most guys just think that IC is close, Modified is medium and full is for ducks. I remember how I used to agonize over one or two thou one way or the other.
And it really doesn’t always matter! Even the experts don’t agree on the pattern percentages for each choke. On top of that, just because you have a .020″ choke marked Modified, that doesn’t mean it will throw a 60% pattern with every shell. I may shoot IC or Full with certain shells. And then there is the normal 10% shot to shot variation in patterns. Or is it as high as 20% if you use a 2-3/4″ shell in a 3″ chamber? Browning says it is. So, maybe these guys who don’t know and don’t test know more than we do.
Bottom line is that chokes give an indication of what to expect on average, more or less, most of the time. If you have an IC and a Mod choke, you have the right to expect the IC to be looser most of the time. How loose is another question.
Now that my diatribe is over, to your question: Obviously a choke that fits the threads in a .725″ bore won’t pattern quite the same as the same choke in a .730″ bore. Something is wrong somewhere. There shouldn’t be a safety issue as the skirt relief should be well over any ganging of tolerances due to the manufacturing process. I say “should”. It’s not guaranteed. I always check my skirt/bore clearance with a dental pick and strong light when I buy a new screw choke.
I’m not sure about the barrel dimensions you were given. The original invector Browning B-80s I had were made with Beretta barrels and had measured I.D.s of about .721″ to .722″, not .725″. I never got around to measuring my original Winchester Pigeon grades and their Winchokes and I never thought about interchanging Invectors and Winchokes. I’d sold those hard-kicking Winchesters before I bought my B-80s. If the Winchester IDs are .730″ as you say and the Browning IDs are the .721″ I measured, there is going to be a performance difference issue when you use the same choke in either gun. .009″ is a lot, especially in the area of the more open chokes. It’s about the difference between cylinder bore and IC and that is a noticeable difference. It just shows that you can’t take anything that is mass produced on faith. What was it someone said about the word “assume”?
If you want what you want when you want it, measure the bore of your gun and then call up your choke maker of choice and ask for a specific numerical constriction. I’ve done this with Briley and they have sent me back chokes that were dead on what I asked for. That doesn’t guarantee any particular exact pattern (see above), but at least I know what I have in the gun.
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)