Theoretical Choke Constriction


Dear Technoid:

I recently “acquired” a 16 ga. SxS and I’m wondering how to tell the choking. I do have an I.D. micrometer to measure bore size about 4″ to 5″ down the muzzle. Without getting into patterning to determine actual choke size, does the 16 ga. choke size (by name as opposed to number) change every .005″ as does the 12 ga.? Is there a standard or typical bore dimension for 16 ga.?

I’m guessing that the choke size would change at something less then .005″ since the bore size is smaller. I’m more curious then serious about this. A “general” explanation would certainly be enough to satisfy my simple-minded curiosity.

Your Loyal Subject,
Terry

Dear Terry,

A measurement 4″-5″ down the muzzle might not be enough. Some of those older chokes could be long. Still, you are probably OK.

Standard I.D. on a 16 gauge is .670″. As I have often said, choke is strictly based on performance. Whatever constriction will put 60% of a certain load into a 30″ circle at 40 yards is a Modified choke. If you keep the same choke, but change the shell so that it patterns 50%, you now have an Improved Cylinder choke. Obviously, this can drive your crazy. None of us have the time to pattern each and every load, so we just trust the manufacturer. A gun stamped “modified” probably throws a modified pattern with some shell, though it may not be with the one that we are using.

I don’ t know all the conventional choke I.D.s for the 16. I would guess thought that they are very close to the 12 even though the bore is smaller. If you are really fussy, calculate it out. I don’t own a 16, so I am not properly motivated.

Example: lets say that .020″ is the standard modified 12 gauge constriction in a .729″ bore. That means that the bore is constricted from .729″ to .709″ to produce your modified pattern. The same percentage reduction in I.D. area applied to the .670″ 16 bore should end up with your 16 gauge modified choke I.D.

It should be percentage of constriction that controls the pattern. At least that is close as I can come to a choke continuum. Shot column length may also be a factor (it is in the 410), but I don’t think it is a major one comparing the 16 to the 12. Anyway, this is my best guess and the price is right.

Boots off. Beer open.

Best regards,

Bruce Buck
Shotgun Report’s Technoid
(Often in error, never in doubt.)

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