Win 1300 choke fit

Win 1300, 20 ga. has 3 chokes.
mod, full and imp. cyl.
The mod. and full screw into the barrel until the knurled part of choke is touching end of barrel. But, the imp. cyl. choke will not screw down and sticks out about 3/8 in. Threads on all chokes feel smooth to the touch and are smooth when screwing into the barrel.
Am I right that the imp. cyl. should screw down to the top of the barrel or is it suppose to extend beyond the barrel about 3/8s of an inch?

Yes, chokes are all the same length.
There is a ridge at the end of the threads in the barrel.