As for the screw in the nose cap, it is a good indicator of an early rifle. Along with the screw, the barrel will generally be short, say 40 inches or so, big bore, with the rear sight about halfway between the RR entry pipe and the breach, with the signature, if there is one, between the rear sight and the breach. If you look through RCA, you'll find a half dozen or so guns with the screw. Some have only the screw in the nose cap, and others have the screw and an iron rivet.
Also, a lug dovetailed into the barrel is the most common receptacle for the screw, though as pointed out by Eric, screwed directly into the barrel is known as well.
Think back a couple months to the Joel Ferree signed rifle posted here.
https://americanlongrifles.org/forum/index.php?topic=69696.0 The barrel is about 40" long, and it has the rear sight about half way between the RR entry pipe and the breach, and along with other indicators, would suspect it's a 1770, or even a bit earlier gun. Certainly, pre Rev War.
Just my opinion of course, John
PS, I suspect some new pictures of the Joel Ferree rifle might show up pretty soon.....