Choke constriction info.
 

I am checking out the bore diameter on a 12ga 30" GH damascus barreled gun using a Skeets Gun Shop dial indicator bore gauge.
Here are the following measurements. Both barrels seem identical within about .0015 at all of the increments.
Increments are inches from the end of the muzzle.

4"- .051
3"- .049
2"- .048
1"- .039
0"- .022
Leaving me with a choke of .029
Is there a constriction chart that will give me the ballpark equations for various constriction ranges? IE, .029= Mod, Full etc.?
Do the above constrictions and intervals sound realistic for an untouched bore as far as the bores not being honed etc.?
Checking wall thickness is next on the agenda.

29 thousands is a full choke

four inches of taper in a choke is not unheard of

as for charts - pick one

https://www.bing.com/images/search?q...tion&FORM=IGRE

but I am confused - a modern nominal 12 gauge is .729 - older Parkers were often a little over bored

are you saying that 4 inches from the muzzle - the bore diameter is .051?

12 gauge chokes....skeet is .004, IC is .009, mod is .018, imp-mod is .027, full is .036, x-full .045 Everyone has opinions, this is what I use for a guide. SXS oho

I came up with improved modified on the sight I saw on the internets.

Does the .017 constriction in the last inch sound normal?

This box contains many of James P. Hayes personal choke reamers. Most all are stamped with either his name, or his initials, along with the bore (12, 16, 20, etc) and are also stamped with dates between 1895 and 1903.
Without having a set of centers, some are difficult to measure as they are five fluted. This collection was given to a friend by Charley Parker, in addition to many other tools. They have since been passed to me. I also have James Hayes chamber rim cutters (all the way to 8 ga.) and a few chamber reamers.

Looking at the choke reamers, what is evident is that the cutting portion of the flights varies somewhat between 3 3/16" and slightly over 4" (20ga.)
There were no specific reamers for specific final choke diameters; the reamer was simply pushed further into the bore until the desired diameter was achieved. With this collection, I also obtained the rods which the reamers were screwed to. These rods have adjustable stops, which allowed the breach face to only move so far in relation to the reamer. The length of taper, logically, for a full choke was close to the full length of the reamer, however, a choke considerable more open would have a uniformly shorter taper.
I do not believe there is any data which supports the belief that there was a "Standard" length of taper. As reamers required sharpening, they were ground, on offset centers, and, consequently the length of the cutting portion, at a specific diameter, would become shorter over the life of the reamer. These tools were likely the property of the individual tradesman, and they may have seen many regrinding cycles. Today, the reamer would simply get tossed to the scrap barrel, and operator would take a new one out of the tool room.

Neet stuff Edgar. What centered the reamer I've reamed bushings but they weren't tapered. Impressive the craftsmanship those fellows had. What did they take the reamer marks out with, a stone hone?

Is this correct or should it be eliminated?
http://www.parkerguns.org/pages/faq/ChokeSize.htm

That's a good question Calvin.
The barrel tubes had been rough bored, prior to the choke reaming. The term 'rough' didn't suggest it was a coarse cut, or unsmooth surface, it merely differentiated the operation from a final polish.
The bore was then given an operation, taking it down to 'near-bore' dimension (varied from early guns of slightly over .750" to late guns closer to today's .729") The last few inches were finished with the choke reamer.
The flights (or flutes) of the reamer wanted to resist cutting into the barrel wall, and naturally sought to move off the wall, toward center. As all the other flights were doing the same thing; seeking a balance in concentricity, the reamer stayed in the geometric center of the tube.
The Sunnen hone, much like a brake cylinder hone, except on a long shaft, with a hollow center allowing cutting oil to flood the area, also stayed centralized in the same manner.
Variation in barrel wall measurements are almost always a result of 'striking' the outside surface of the barrel; the operation of prepping the barrel for final finish.

Robin, those figures have been the standard for years and should not be eliminated. Just my $.02.

Edgar, that is some really neat stuff.