How to determine choke?

[JW in Ohio]

I have an old Sears 16 gauge that has no marking as to the choke. Can this be determined by simply measuring barrel internal diameter with a caliper, or is it more involved than that? If it is a set measurement, what are they for the different choke settings?

Is there some other way?

 

[mete]

While you can measure the choke that really doesn't give you the whole picture. You have to pattern the gun regardless of the choke since there is a great variation from ammo to ammo and gun to gun. The pattern is determined by checking at 40 yds ,what percentage of shot goes into a 30" circle.

 

[9mmMike]

Choke is really better defined as POC (Points Of Constriction).

Measure the bore and the choke and subtract. This is the real choke.

Most manufacturers use .729 as "standard bore" but it seems to be an approximate to say the least.

There is a table floating around here somewhere but a .010 difference would generally be considered an IC (Improved Cylinder) choke. I think Mod is .020.

For example:

I have a barrel for my 870 that was marked as IMP CYL. Measurements showed the real deal to be .737 bore with .014 poc. Closer to Skeet-2 IMO but we'll let that one go.
I had the barrel back-bored as part of a roll-your-own experiment so now we're looking at .022 poc which is closer to MOD.

The muzzle end is still the same size and yet the choke (POC) is different.

Never trust the stamp on the barrel, if there is one.

I will try to find the chart and post it here unless someone beats me to it.

Mike

 

[halvey]

I'd bet the farm a Sears 16 ga has a full choke.

 

[Hawken50]

some good info here.

Chuck Hawk's choke page

 

[9mmMike]

Good chart Hawken50.

 

[f4t9r]

good chart and 9mm Mike thats some good stuff you posted to

 

[Hawken50]

look around on that website. there's a metric a$$ ton of good stuff in the free section.

http://www.chuckhawks.com/index2.guns.htm

 

[JW in Ohio]

Chokes seem have lots of variables

Thanks for all the replies guys. The Chuck Hawk site is very good and explained clearly what I have suspected, that chokes are a determined by many variables. Even a change of ammo brand will result in a different percentage of hits in a 30" circle, thus officially making it a different choke in the same gun. And then different gun makers use different standards. Shotguns really are "more art than science".