doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Choke measurement question

choke measuring 33th. would be? Improved Mod or Full?

In a 12 ga. .033" is considered full choke, Mike.

At least since 1883 - Sport with Gun and Rod in American Woods and Waters by Alfred Marshall Mayer
https://books.google.com/books?id=IJcCAAAAYAAJ&pg=PA781&vq
The choke-bore now almost universally adopted by gunmakers is as follows: Taking a twelve-gauge gun as an example, the construction of the bore from the front of the breech-chamber to within one and a half inch of the muzzle amounts to about 1/100 of an inch. At one and a half inch from the muzzle begins a sharp contraction which, in the length of one inch, equals 25/1000 of an inch. The last half inch of the bore is a true cylinder.
.010" + .025" = .035" constriction = "choke bore"

That would be the 'taper bore' which was not commonly used by U.S. makers, but often used in advertising



In the 1907 edition of Greener's The Gun and Its Development .030" - .040” is Full or “Choke Bore”
https://books.google.com/books?id=3HMCAAAAYAAJ&pg=PA251

With modern premium shells it is very likely to pattern the 'Full' standard of 70%

I have often referred to this chart, considering it to be one of the most comprehensive I've ever seen.

https://www.hallowellco.com/choke_chart.htm

It shows clearly how much less constriction is needed to acquire a choke percentage as the bore gets smaller.