DO NOT INSTALL a standard Winchoke or Invector in a .743 barrel. The standard Winchoke is designed for a .730 bore, Invector .725 bore. If you fire your gun the shot and wad will hit the rim of choke tube. BYE BYE Barrel, and maybe you.
I've just measured a handful of Winchokes and if you had a bunch to choose from, that might have the correct constriction, you could get lucky. The "mouth/entrance/throat" or whatever you want to call it, bore at the beginning of the tube is .743"-.744" on a couple of them. But they're only 1.5" long, for the notched versions which would go into your barrel.
If I were you, I'd get ahold of Steve Baldwin in OKC, he's made a ton of these with whatever bore you want, I've got a set of "Winchokes" he made that are 3" long and the throat on them are about .750". He'd make them whatever length/bore/constriction you need.
This is the latest contact info I have for him:
2828 NW 10th St
Oklahoma City, Oklahoma 73107
Oh, and, when Stan Baker did the "swaged" barrels on Winchesters, the tubes he used on those would most likely fit your barrel. I'm about 99% sure those were "Teague" chokes, made in the UK. They had/have a full taper to the muzzle without a parallel section. Don't look down your nose at them either, they patterned exceptionally well.
I think I might have some tubes as you describe. They were on a Baker
1100 barrel and were retired when the barrel tang developed a crack. Stan's
grandson who was continuing the business didn't want to mess with the
barrel suspecting it had poor metal to begin with. This happened about 4 years ago.
I'm wintering in Texas and won't return home to Michigan until mid April when I can re-examine them. Email is [email protected] Judging by
earlier posts, you are probably already set. Just thought I'd add.
ATA John, I have a BT-99 with a full set of choke tubes like the one you show in the picture. At the time Stan made them, he said they were the same as the Invector Plus tubes only the Invector Plus tubes were a little longer & thus would stick out the barrel a bit. John