Best method is going to be measurement with calipers or coke gauge. What they may have been when leaving the factory is one thing but afterwards anything goes. Rough gauge for 12 gauge full choke is will a dime enter the barrel end on edge. Yes it enters not a full choke, no it doesn't enter then its probably a full choke.
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My old Model 311A 20 ga. had M/F chokes. What a great old shotguns they are. I bought mine used in the early 70's and shot it up till a few years ago when I gave it to my son. I replace it with a nice O/U. Didn't take me long to really miss the double triggers of the old 311A. What great solid, dependable old shotguns they are.
311 chokes
The dime trick has been around for years and doesn't really work. Choke is the difference between the cylinder bore and the muzzle bore. The best description of how it all works is Patrick Sweeney's Gunsmithing: Shotguns from Krause Publishing. For 12 ga. should be .729 inches. Full choke is .035,IM=.025, M=.019, Skt2=.012,IC=.009. If you have a barrel that was bored at the end of the life of a hone the cyl bore may be as tight as .715" so a Skt2 choke would be tighter (smaller dia.) than the next barrel off the line cut with a new hone that cuts a true .729" bore. Barrel #1while tighter at the muzzel than barrel #2will give Skt2
patterns. Barrel #2 will give full choke patterns. That's the theory anyway.
Shooting at a pattern board is the only way to tell the choke of a shotgun. You can buy a bore dial gauge, about $450, and measure the bore and choke diameters. That will give you a better idea of choke of a shotgun but I'v got a 870 that will shoot full choke patterns with Fed.#6's and mod choke patterns with Rem #6's, 3" mag. So you still have to shoot to know
then write down the results. I trusted my memory on the buckshot the 870 preferred and hit a deer and didn't recover it. Anyway get Sweeney's book and read the chapter on chokes it's worth the price.
The dime trick has been around for years and doesn't really work. Choke is the difference between the cylinder bore and the muzzle bore. The best description of how it all works is Patrick Sweeney's Gunsmithing: Shotguns from Krause Publishing. For 12 ga. should be .729 inches. Full choke is .035,IM=.025, M=.019, Skt2=.012,IC=.009. If you have a barrel that was bored at the end of the life of a hone the cyl bore may be as tight as .715" so a Skt2 choke would be tighter (smaller dia.) than the next barrel off the line cut with a new hone that cuts a true .729" bore. Barrel #1while tighter at the muzzel than barrel #2will give Skt2
patterns. Barrel #2 will give full choke patterns. That's the theory anyway.
Shooting at a pattern board is the only way to tell the choke of a shotgun. You can buy a bore dial gauge, about $450, and measure the bore and choke diameters. That will give you a better idea of choke of a shotgun but I'v got a 870 that will shoot full choke patterns with Fed.#6's and mod choke patterns with Rem #6's, 3" mag. So you still have to shoot to know
then write down the results. I trusted my memory on the buckshot the 870 preferred and hit a deer and didn't recover it.
Anyway get Sweeney's book and read the chapter on chokes it's worth the price.
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