Lefever bbls were choked on the "Taper" principal, IE the entire choke section was a taper with no paralell at the end. A full choke normally had a taper of at least 4". I can't prove it but highly suspect that all chokes were cut with the same reamer by simply running it deeper thus giving a shorter taper with less constriction for less than full. Unless the choke was subsequently reamed as well as the bbls being cut, I highly suspect your bbls originated as 30". Either way, while the collector value has been reduced you should have a very useful gun. My FE SN 38,025 also has chain damascus bbls. Though this pattern is more commonly associated with the E grade they do show up on the F's sometimes, but not the most common pattern.
Enjoy it.
