"pyotr filipivich" wrote in message
...
"Steve W." on Wed, 23 Oct 2019 18:18:13 -0400
typed in rec.crafts.metalworking the following:


At the moment I'm thinking a wooden bench then a single slotted bar
and
an adjustment pin system at one end to select twist rates. I made a
smoothbore .50 a long time ago and it shoots real well considering.
The
bench and the rest are the easy parts. The big thing is the cutter
advance, current thought is a long tapered wedge with a fine thread
adjustment.

I recall reading about using paper or similar thin shims. But the
wedge with fine thread might work too.

May not be automatic at first but I'm not running production
levels.

For real fun, work out how to do a "progressive twist" - where the
rifling twist gets higher the further down the barrel the bullet
goes.
--
pyotr filipivich
"With Age comes Wisdom. Although far too often, Age travels alone."

A lost method to lay out mathematical curves on a long cylinder was
discovered scribed on the unfinished wall of a Greek temple when it
was excavated. Had they finished the temple the scribed markings would
have been polished off. It's similar to the way I learned to lay out
the patterns for sheet metal ducting transition pieces, and the
full-sized ribs of sailing ships from the carved half model.

The desired curve would be drawn at full diameter but compressed
mangeably small in length and divided by eqully spaced lines. For
example it might be part of a parabola, the integral of a linearly
increasing function.
https://www.wikihow.com/Draw-a-Parab...Straight-Lines)
Next to it the full size outline of the cylinder, a temple column,
would be outlined and divided vertically by the same number of lines,
spread out evenly. Then with dividers the position of each
intersection of the curve and the verticals would be transferred from
the small drawing to the full-sized one, and connected by scribing
along a thin wooden strip bent to match them, giving the effect of
drawing the curve accurately with impossibly huge instruments.
https://en.wikipedia.org/wiki/Entasis

The same method could lay out a progressively tightening spiral on the
rifling guide, by transferring the heights of the profile of a curve
to the guide with a fine chain.

A sine bar rifling machine can be built strong enough to drive the
cutter directly from a straight or curved template, instead of guiding
a pencil to draw the spiral groove on a wooden cylinder.