Yes geometry matters. When I made mine a based it on the diagram in MB mag. I believe it was in the early 90's. I then made some changes that I thought would improve the design. When I picked up a file one day I thought, man that would make a good choking tool with a few mods and I used it to make the cutter and soldered it to the key stock. A lot of these dimensions depend on the gauge and the amount of shot you plan to use
A. This will vary slightly, depending on the depth of the jug but generally speaking you want the shot column to be fully contained in that 'CHOKE" to work properly. In other words, A should be the length of you shot column. If you look at my tool there is a brass pin that rides against the muzzle to position the choke in the bore.
B. This is a dimension that was really dictated be the taper of the file but generally speaking you want the taper "into" to jug at a slower taper than the taper coming out of the jug. It will also vary depending on depth of the "jug".
C. This OAL of the jug should also be the length (or longer) than the shot column.
D. OAL length is not really important, if you follow the two above statements it will come out OK.
E.I believe the choke I have pictured on ALR was for a 12 bore, and it probably could be used on bored from 14 bore to 11 bore.
F. This depends on how much choke you want , but generally speaking, 8 to 10 thou. is IMP. 16-18 thou is MOD and 24-26 is Full. I have never choked past .026 and get excellent results but I have heard of others choking up to .035 too.
One point to remember is that the shot column will expand to fit in the jug and the wads need to expand too so there is no loss of pressure. Hard cards or thick wads may not expand sufficiently. It may be necessary to go with paper, cloth of wasp nests if you go for a full choke.
Let me know if I can answer any more questions, Ed
