Chambering one of those cartridges in a match, Bentz, or other short chamber forces the mouth of the case hard into the rifling leade, and that increases the grip of the case on the bullet for a dramatic increase in chamber pressure.
A - The body diameter of the chamber at its mouth B - The body diameter of the chamber at its forward end C - The length of the chamber body D - The diameter of the cartridge rim seat in the chamber E - The diameter of the forward end of the body section of the chamber just before it angles slightly inward to form the leade, which funnels the bullet into the rifling.
The square rod was twisted to the desired rate of rifling pitch and the cutter box was affixed to its end.
Since the barrel had to be firmly clamped into position on the early rifling benches, the entire tooling assembly had to be capable of being positioned in discreet radial increments in order to cut multiple grooves into the barrel.
The older l:38-twist barrels had rather shallow rifling
, and they could begin to open groups once some wear sets in.
Here are my experiences with my Jeffery 8-bore ball and shot gun with invisible rifling. Initial shots with a conical bullet of 1345 grains and a round ball of 900 grains showed the target patterning a good example of what drives double rifle men to drink.
The invisible rifling was where the answer was to be found.
The bullets were .002" undersize, the many bands allowed metal to flow when it was cut by the rifling, and I began with a slow velocity and worked up to the factory regulated velocity of 190fps.
However, I did notice the rifling was very shallow.
pitch depends mainly on the bullet's length and speed.
Mike filled the bores full of charcoal so no oxidation would scar the rifling
, before evenly heating the barrels for 35 minutes over a bed of burned-down coals.
If you visit the gunsmith's shop in Colonial Williamsburg, you will see a massive, wooden rifling
machine that was used to manufacture rifle barrels during the Revolutionary War.