In some of the old catalogs there is reference to "Multiplied Choke Boring" and that most of the guns that left Hunter Arms or even earlier L.C. Smith Maker were bored this way. I tried to figure out what was meant by this and reading articles didn't really tell anything. I made up some bore gages in 12 ga, and in most literature about bores from L.C. Smith is that the bores were from .729-.732. In a few that I have checked the older ones seem to be less. A good example is a circa 1899 Grade 2E with 30" Crown Steel barrels. Bore in right barrel is .724 and goes in 13 5/8", left barrel .724 goes in 17". Bore gage of .722 goes in 26 9/16" to taper of choke and in left barrel .722 goes in 27 3/8" to taper of choke. Muzzle end choke right barrel mikes up .686 and left choke is .683. The interesting thing is that it you used only a dial indicator like Skeet's or Brownell's you would get a reading of .017 and .015 thinking you were at less than modified.
Are these tapered readings what is considered Multiplied Choke Boring, even though it is not in the choke area it is constricting the shot down the barrel. What are your thoughts.
Also to me having the chokes read with a dial indicator or even with a telescoping gage is not really telling you what the true chokes are if you do not know the bore size. If you go back to my readings you will see that now the difference is from .723* to .683 a difference of .040 or full choke compared to .015 with indicator. Also indicator was set up 10 3/4" into barrel from muzzle and then zeroed, withdrawn and read.
Also the bore diameters of early 16 ga. were .650 and I believe that changed around 1936 to .662 so there is another reason to know your guns bore diamter.
*.001 was added to reading because size to size will not fit.