No4t Cocking pieces, which is best.

[Beerhunter]

I'm not sure if I am restating the obvious here but the reason that some No.4Ts have the rounded cocking piece is because they were built from "Trials Rifles", which have that style of cocking piece - as simple as that. (That is to say, other than the usual: that was the one on the armourer's spares box during a repair.)

As to the "experts", even they can't "get around" the physics. At least not without some help from Gene Roddenberry.