Shotgun question

[bns]

I recently bought a smith&wesson 12 gauge and it's not marked as far as the cylinder whether it is full modified or improved. What I am wanting to know is if there is a way to tell.I know they used to say if you could stick a particular coin in the end of the barrel it meant it was one or the other, but don't remember what coin that was. Can I get a little help here please?

[trailer]

If I"™m not mistaken, the test is a dime. If you can"™t fit a dime at the end of the barrel it"™s a full choke.

[DM]

No matter how it's marked or what a dime will do, you won't know what you have untill you take it out and shoot at pieces of open news paper to see how it patterns! (at the ranges you will be shooting at while hunting) Use the ammo you want to hunt with, and check it yourself so you know for sure!

Drilling Man

[Rebel Hog]

Gauge measurement in relation to the diameter of the barrel:
10 gauge = .775 inches
12 gauge = .729 inches
16 gauge = .662 inches
20 gauge = .615 inches
28 gauge = .550 inches

[Rebel Hog]

[align=center][/align]

[Rebel Hog]

Subtract the reading form gauage size!








These are measured at a distance of 25 yards. The following chart can be used as a general guide.
[align=center]



Name
#%
Constriction

Cylinder Bore
40
.000

Skeet 1
50
.005

Improved Cylinder
50
.010

Skeet 2
55
.015

Modified
60
.020

Improved Modified
63
.025

Full
65
.030

Extra Full
68
.040

Super Full
70
.045

Turkey
70+
.045+[/align]
The above chart is based on using premium field loads with #8 shot. Generally the larger size of shot you use the less degree of choke is needed to get an equivalent size pattern. High velocity or magnum loads normally do not pattern as well as lighter loads. The same load by different ammunition manufacturers may not pattern the same. As you can see, there are many things that can cause a shotgun to shoot a different pattern with the same choke constriction. Most chokes will shoot a pattern reasonably close to the marked size, but the only way to be absolutely sure of what your gun is doing is to "pattern" it. Use the loads you plan to shoot and try different chokes to get the pattern you want.

[underdog]

One problem, Hog. The barrel diameters vary quite a bit among the manufacturers.

You are correct that the amount of choke constriction in a barrel is the difference between its bore diameter and the constriction at its muzzle. The best way to measure both is with a dial caliper as you showed. In a 12 gauge as an example, while standard bore diameter is supposed to be in the neighborhood of .729 to .730 inch, barrels from various makers can range anywhere from .720 to .735 inch, and those that have been backbored can be even larger. Assuming that the correct amount of constriction for, say, Full choke for the 12 gauge is .040 inch, it is easy to see how actual inside diameter at the muzzle can vary from .680 to .695 inch for that designation.

BNS, since you probably don't want to buy a caliper to measure one time, visit a gunsmith that works on shotguns and he can tell you the amount of constriction.