Actual choke Dimensions

Improved Modified is great for handicap singles. The actual measurement of the choke is meaningless unless you also have the bore measurement to compare it to because different manufacturers use different bore sizes and the degree of choke is a result of the difference between the bore size and the choke size, which is smaller of course. If the choke on this gun hasn’t been altered then it will be fine for handicap, pattern different brands and types of ammo to find out which gives you the best pattern. In general, unless you are a 26-27 yard shooter this is probably your most useful handicap choke. K I S S
 
Falconflyer has very good advice
Bore diameter on 12 ha will be .725 to .735 and even up to ..740 depending on gun manufacturer
 
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Thanks for the compliment Struff55, I'll try not to let you down! :)

The choke marking on the barrel is just that... a marking on the barrel and like Ashcroft said, the actual measurement is meaningless without knowing the bore diameter to compare it to. So the barrel marking is really only a guideline and you won't know what you have unless you pattern the gun with the ammo you intend to use then count the holes and do the math. Most European guns have the bore diameter stamped on the barrels for reference but that was never Brownings thing as far as I know so to know the ID of the barrel will require some measuring instruments and even then it's purely academic.
Getting technical with shotgunning often leads to frustration and laying blame to the equipment, the best thing to do is go out and break targets and if the choke measures .690 then I guarantee that Bt99 will break targets from a long way back!
 
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Falconflyer said:
Thanks for the compliment Struff55, I'll try not to let you down! :)

The choke marking on the barrel is just that... a marking on the barrel and like Ashcroft said, the actual measurement is meaningless without knowing the bore diameter to compare it to. So the barrel marking is really only a guideline and you won't know what you have unless you pattern the gun with the ammo you intend to use then count the holes and do the math. Most European guns have the bore diameter stamped on the barrels for reference but that was never Brownings thing as far as I know so to know the ID of the barrel will require some measuring instruments and even then it's purely academic.
Getting technical with shotgunning often leads to frustration and laying blame to the equipment, the best thing to do is go out and break targets and if the choke measures .690 then I guarantee that Bt99 will break targets from a long way back!
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I have seen more than a few people changing chokes and loads, addiing hiviz bars, and constantly adjusting the stock, rather than working on the real reason that they are missing, which is them, not the equipment.
 
stubblejumper said:
I have seen more than a few people changing chokes and loads, addiing hiviz bars, and constantly adjusting the stock, rather than working on the real reason that they are missing, which is them, not the equipment.
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It's funny as heck some times. I've had guys tell me that they purchased after market tubes because the gun manufacturers tubes were cut a couple thou off what the shooter thought they should be... never realizing that it's all relative to bore diameter. When I inquired if the guy had patterned the factory tubes the answer was no. The manufacturer didn't cut the tubes precisely enough and that was a good enough reason to blow several hundred dollars on tubes. Then there's the guys who want choke tubes that fill in between the standard size chokes so they have a bag full of tubes in one or two thou increments and are constantly changing tubes, crazy but true!
 
Nominal bore size for a BT-99 according to the internet is .740.
You won't notice any difference at all out to 25 yards and you can still break targets out to 27 if you are precise. I shoot IM out to 25 yards and manage to break a few targets now and then.
 
A double with different bore sizes between the two tubes is not unusual, especially on older guns. Most people have no idea what the actual inside diameter of their barrels are and don’t care as long as the gun does what they expect it to do. A shotgun ( with shot, as a SHOTgun) is neither a long range nor a precise firearm, it is intended for fast moving short short range targets. Trying to apply rifle logic to a shotgun only results in frustration. With a rifle (or pistol) the goal is to be precise, to hit a specific point. With a shotgun the goal is to hit the target anywhere, precision isn’t an asset. Over the last century and a half an unbelievable amount of experimentation with the internal dimensions and profile of shotgun barrels and with shotgun ammunition have resulted in perhaps a 10-15 yard gain in maximum effective range with some combinations at the expense of smaller short range patterns that result in more close range misses. There are no absolutes with shotguns, a change in one factor always results in an opposite change in another factor.
 
bdft said:
Nominal bore size for a BT-99 according to the internet is .740.
You won't notice any difference at all out to 25 yards and you can still break targets out to 27 if you are precise. I shoot IM out to 25 yards and manage to break a few targets now and then.
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Bore diameter depends on the year it was made. The guns made from 2001 on we’re over bored and are supposed to be .740 but they seem to vary from about .736 to .742. Prior to 1995 (production was stopped from 95 to 01) the bores were tighter than that but I don’t have exact numbers.
 
I guess what I was trying to say in my last post without actually saying it is that I would find it hard to believe his gun has a .740 bore with a .690 choke and is marked IM. 50 thou constriction would be equivalent to extra, extra full on an over bored barrel. Old Brownings are bored fairly tight and .690 is a common choke diameter for a full choked gun so I think this is probably an older gun.
 
Thanks for all the replies. I did buy the gun after I posted originally and when I got the gun the barrel was marked as a full choke so it’s a full choke. Shoots nice patterns with all the loads I’ve tried. Got a couple 50’s with it actually, just need to break 75. I also bought a model 12 trap a few weeks ago and have just been playing with that. What a tight choke on that gun. Absolutely just smokes targets. I’m torn between the two. I’m going back to the BT this weekend though.
 
Patterning a gun will tell you more then any amount of measurement. I have the tools to measure bore diameter and choke diameter to give an accurate measurement, but patterning will tell you what those measurements do with your ammo. My experience opening up chokes and installing screw in chokes says there is a wide variation in bore diameters.
 
Bore size will be .725 to .735 if you have a bore gage you could measure the bore of the particular gun then measure the muzzle and that will tell you the degree of choke for that gun . Will that make any difference in your scores not likely . It may put your mind at rest knowing the specific choke .
With 30 years of competitive shooting behind me I know for certain I never missed a target because of my choke or because I didn’t pattern my gun or because I was using no 7.5 instead of no 8’a
 
My buddies son was totally convinced when his favorite aftermarket choke cracked and split this fall that installing another choke to continue his hunt had significantly changed how much he had to lead to kill a goose. That was a new take on chokes to me. Then he was really bamfoozled when he found out I was shooting geese at the same distances as his long range choked 12ga running 3.5" BB ammo with my 3" 20ga running #2's through an IC choke and folding birds just as well. Lol
As for IM choke for trap it's all I shoot in my TMS for 16yd and handicap. My handicap is currently 25.5 and I shoot 1oz 7.5/1250fps labelled factory loads.
 
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