Chokes are funny things!

[PaulF70]

I have a (gorgeous) Pedersoli SxS in 12. I was unsure of the choke so bought one of those choke-telling insert thingies.

It tells me that the left barrel is choked "1/2" which according to this chart I found is .020" which is Modified.

All good so far. Here's the kicker. I bought two full choke inserts for my Ruger Red Label O/U and installed them. The same tool measures these as "1/2" - Modified - also.

What is going on here?

 

[Brokennock]

Choke is not actually a fixed measurement of the bore at the muzzle. Constriction choke is the constriction of the inside diameter of the bore at the muzzle,,,, in relation to the rest of the bores diameter. This is why a full choke trap gun that is back bored shoots a tighter pattern than a full choke field gun that is not back bored.

The Ruger Red Label chokes are sized based on Ruger's known inside bore diameter. That same mod choke might shoot like a full choke if it were screwed into a gun with a larger bore diameter.

The choke measurements we see listed and that are used to create those choke gauges are a "rough idea" within given parameters.

 

[PaulF70]

Ok, I get it now. Choke is relative to the size of the bore, which varies (by manufacturer, etc.)..

That makes this choke measuring device I have a bit useless.

 

[Sparkitoff]

Your muzzleloader shotgun will be marked in mm - like 17.2 or something like it. Convert it to inches and there's your nominal bore diameter. Subtract the constriction and there's your choke. On the other shotgun, you'd need to measure in front of the chamber to get the nominal bore diameter. The proof houses measure 9-inches from the breach and at the muzzle.

 

[Brokennock]

That makes this choke measuring device I have a bit useless

Somewhat, but not completely.
It still gives you a rough idea of where you are. Just not how it will shoot.

A lot depends on load. Both components and volumes of shot and powder and amount of wadding, and if a cup is used.
My favorite antique 16 gauge SxS is "choked" mod and full. I usually bird hunt with very open chokes when hunting with your typical modern shells.
But, using special shells that are of the correct length for the 2 1/2" Chambers and no shot cup, the gun serves me quite well.

 

[PaulF70]

The world is too complicated.

We need to destroy everything and start again. In the next version of The World all shotgun bores will be of uniform size.

 

[Lorne Johnson]

Ok, I get it now. Choke is relative to the size of the bore, which varies (by manufacturer, etc.)..

That makes this choke measuring device I have a bit useless.

Not useless, but limited. Another issue is that the choke constrictions used by many manufactures changed when steel shot came into use. So there are a lot of variables.