Jug Choke?

[SPEEDY]

I was looking at putting screw in chokes in the barrel I cut down the other week but then I remembered Jug chokes and that would be perfect. The trouble is I can't find any information about length from the muzzle, depth and side angles.
For a anyone here know much about them?

I have heard a lot of blokes doing them at home with break cylinder hones and similar and thought that might be fun to do, although I would rather get a loan on a lathe and do it with a boring bar.
I thought 1" at -.020 depth with a 25°-30° taper for 1/2" on the ends would be about right.
And strangely about 1" back from the muzzle, I would have thought right at the muzzle but it seems you want it back as much as 2" from what if pieced together.