No, there's no secrets at all. You just turn them down and strike them up so they look right.

I recontoured my Mannlicher this evening, it must have been made by a German. All straight lines. I finally had enough of looking at it and stuck it in the lathe. The way to get the barrel to have the correct look is to turn a "swamped" taper. That is, instead of a straight taper it's got a very slow radius (sort of). I really don't know if there's a formula or not. I can tell you my breech and muzzle dimension, and the rest is made to, again, look right.

The barrel needs to swoop down from the breech in a gentle curve to the muzzle. This makes the barrels appear longer and slimmer than they really are. A straight taper is an obsolete no-no, the center of it will actually appear fatter. And a series of tapers will show transitions when looking down it, instead of being a smooth swoop. A shotgun barrel, and some rifle barrels (especially Alexander Henrys) will be a little larger at the muzzle, and have a waist in the barrel which accentuates the swamp.

Of course, the barrel must be struck up and polished perfectly, as the slightest bobble will show up.

I have a Mannlicher barrel that needs that now.....

Hopefully this will make sense to you.