I just opened up a couple of Ponsness Warren Shot bushings on my lathe. How much to open was guess work & to increase drop 1/16 oz does not take much. I made a tool to hold 280 grit paper. Put the bushing in the 4 jaw indicated center and lapped. Few papers through the bushing took it out weighed a shot drop, and chucked it up again. Slow part is checking then re-chucking, half a dozen times but came out perfect.
Next one I made up a boring bar and cut the first step, it dropped right on desired weight so I omitted the lapping. Bushing works fine inside surface is not smooth. Not a choke job but the principal is the same.
Seems to me to do a choke right same method, lapping and testing is the way to go. Proper lead lap not my quick paper rig. I say lead because that's how rifle barrels are lapped. Might be a smooth bore large hole stone would work better. Very labor intensive all the set up test then set up again. Although a lap cuts fairly fast if it fits well and carries aggressive grit. Going slow and checking progress on the pattern board could give good results. That rig in the photo would be a good set up to open with a lap. Appears he can remove and re-set fairly fast.
More than one way to do a job all they all work. I am probably over thinking it.
William
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