Matching Bore To Choke


Hi,

How important is it to match the choke to the bore size? Both Angle Port and Seminole had Beretta chokes for bore sizes ranging from .720 to .740. Big difference. My wife has a Beretta and wants to know. I need chokes for my K-80 and will go with either brand as Briley chokes cost more anyway. It seems to make sense to have a nice smooth bore at the end.

thanks,

Joe

Cheyenne, WY

Dear Joe,

If the choke isn’t matched to the bore size, you don’t get the amount of constriction designated by the choke.

Example: Beretta Mobilchoke 12 ga barrels are right around .722″ or .721″. Skipping any issues with skirt dimensions, if you want a typical modified choke constriction of .020″, then you want a choke that measures .722″ minus .020″ or about .702″. A couple of thou one way or the other doesn’t make the slightest difference, but ten thou would. If you stick a choke intended for a .720″ bore gun into one with a .740″ bore, not only would you be getting about .020″ more choke than you figured on, you could also possibly run into a choke skirt that protruded into the bore. Baaaad move. Your next shot will have 1-1/8 oz of shot and about 1-1/4″ of steel choke flying through the air.

As to smooth and rough chokes, many people believe that a rough choke retards the wad and produces better patterns. Dunno about that myself. I always liked smooth chokes as they stay cleaner and don’t build up as much. One thing that you do want to avoid is a large “step” between the barrel bore and the relief at the skirt of the choke. The skirt of the choke is sunk below the bore of the gun for obvious reasons, but you don’t want it so low that it creates a valley. Cheap choke installations meant to cover up for a ganging of tolerances usually have large skirt drops. Really high end choke installations like Teague have a drop so slight that you can barely see it. Close tolerances here mean that there is less of a “bump” when the shot load whistles by.

Any “over the counter” choke will have a considerable drop at skirt because it will have to safely fit any gun made to accept those chokes. If the choke skirt protrudes up into the bore, the choke will shoot out. To prevent this the choke makers play it extra safe and really back that choke skirt away from the bore. Not good ballistically, but it makes it easy to mass produce the choke to fit any gun.

It’s all a compromise of price. If you want to get custom chokes matched to your barrel, that’s probably slightly better, but more expensive. None of it makes any sense anyway unless you do extensive pattern testing. Remember that true choke designation is based on PERFORMANCE, not on any particular choke measurement. If a choke with .010″ constriction (nominally an IC choke) patterns 60% in your gun with a certain shell, then that’s a modified choke, not an IC. It’s the performance that determines the choke, not the constriction. It’s just that most shooters won’t bother to pattern their chokes so they believe that they are getting whatever is stamped on the choke.

The best advice I can give is to pattern what you have and see how that works. If it’s good, stop there. If not, then pay the money for the aftermarket chokes. Just throwing money at the pattern won’t always improve things. You may be throwing out the better choke. Also, just because a choke doesn’t perform as marked, doesn’t mean that the pattern it does give you isn’t a good one. You just have to remark it.

The older Beretta Mobilchokes and Browning Invector and Invector Plus chokes definitely weren’t the best, but some did pattern well. You just had to do some work to find out what was what. The new Beretta Optima Bore chokes and new Browning Midas chokes (made by Briley) have better tolerances and a longer design which works better with the tighter constrictions. These features give you a better chance in the choke lottery, but their ain’t no guarantees. You absolutely must pattern your chokes with your shells unless you want to rely on blind faith.

One final thought. All screw chokes are a compromise in efficiency. Proper choke design increases length as the constriction increases. A solid skeet choke is quite short, while a solid full choke can be 5″ or more long due to longer leads and parallels. Screw chokes are all the same length, so there is some ballistic compromise for your convenience. For most shooters, the slight compromise in pattern quality is worth it. For some who always shoot at the same distance, they want to absolutely optimize their patterns and prefer fixed chokes.

Best regards,

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

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