I remember reading that at one time, Winchester used a reamer that was cut with a very wide radius and they used the same reamer to cut all the various chokes, simply running it through a bit farther, for more open chokes. There would be no parallel section. It was also stated that chokes with the more abrupt tapers would produce a desired choke with less constriction. This makes sense to me, as my favorite explanation of how choking works is by deflecting or accelerating the pellets inward, as they hit the constricted area. Something like hitting the rail at a shallow angle, on a pool table.
My experience with Lefevers(not extensive) is that they have all had tapers around 4" long, as 2P stated. To cut chokes with no parallel section, what could be simpler than using the same reamer for all, depending on how far it was run through, to give the desired constriction?
Teague chokes make a big deal of their "continuous taper", like they have invented something new.
Opening chokes with a reamer leaves a parallel section, length depending on how much constriction is removed. I have not observed this to be a problem. The resulting patterns seem to match what the finished constriction would suggest it should, regardless of how long the parallel section turns out to be. Theoretically, at least, if the parallel was long enough, the resulting patterns would be cylinder. I have not observed this. Like Miller, I believe a continuous taper, from chamber to muzzle, WOULD result in cylinder patterns. I remember reading that this was tried, in the early development of chokes for muzzle loaders, and the results were cylinder. In order for choke to work, it obviously needs some abruptness.
