gyrine, I have a K80/M32 top single done and stamped "Stan Baker Seattle Wa." on the barrel. I measured the barrel to be a .748" bore and the 2 chokes are a .720" (.028" constriction) and .705" (.043" constriction). The barrel has a 3/4" dia. weight, 3 1/2" long on the bottom barrel, sticking out in front of the forearm. The rib is approximately 3/8" tall at the back (chamber area) and tapers down to approximately 1/8" at the muzzle end. It is 3/8" wide at the back and 5/16" wide at the front. There is a 2" long "ramp" (not a hump or step) from the top latch area to the 3/8" tall start of the rib. The rib looks to have a area under the bottom side of the rib that would allow it to "grow" when it gets hot. I "tried" to take a picture of the reliefs, but hard to photograph, at least for me that is! The porting is "possibly" Angle Port (not sure, don't know that much about the different companies), but there are 3 holes, then a small gap and then 8 holes. Angling forward the are 3/32" wide x 3/16" long, same width and radiussed at each end. Thought I could shoot this top single like I did my old Winchester Diamond Grade top single, but I have been shooting a K80 un-single for so long now, I will sell this piece of trapshooting history for $1200 plus shipping to you, if you are interested. I have some pictures I can send if they will help.