05-29-2015, 04:44 PM
If the ID of the smoothbore is .256 and then one cuts the rifling, the peak pressure is likely to go down, along with a likely mild decrease in velocity.
If the ID of the smoothbore is 0.264 and then one installs a fresh barrel, then the peak pressure will go up a bit with a mild increase in velocity.
In the first, case, the bullet has to be swaged down to go from the groove diameter of 0.264" to the bore diameter of 0.256" which makes the initial pressures higher.
In the second case, no plastic work is done on the bullet so the initial burn is at very low pressures but we still have a good gas seal. I don't know whether the difference between a perfect seal and the arguably imperfect seal one gets with conventional rifling is enough to make a difference though.
What would be really interesting is to extend the polygonal bore idea to one where we have rounded ridges and valleys with perhaps .003" between the diameter of the peaks and valleys with most of the circumference close to 0.264". This would have minimal plastic work done to the bullet and likely keep the better gas seal claimed by the proponents of polygonal bores.
That scalloped barrel would likely accommodate larger powders with burn rates slightly faster than the current optimum powders too.
Now that I've done the 'invention description' I seem to recall having seen a scalloped bore before but don't remember where!
If the ID of the smoothbore is 0.264 and then one installs a fresh barrel, then the peak pressure will go up a bit with a mild increase in velocity.
In the first, case, the bullet has to be swaged down to go from the groove diameter of 0.264" to the bore diameter of 0.256" which makes the initial pressures higher.
In the second case, no plastic work is done on the bullet so the initial burn is at very low pressures but we still have a good gas seal. I don't know whether the difference between a perfect seal and the arguably imperfect seal one gets with conventional rifling is enough to make a difference though.
What would be really interesting is to extend the polygonal bore idea to one where we have rounded ridges and valleys with perhaps .003" between the diameter of the peaks and valleys with most of the circumference close to 0.264". This would have minimal plastic work done to the bullet and likely keep the better gas seal claimed by the proponents of polygonal bores.
That scalloped barrel would likely accommodate larger powders with burn rates slightly faster than the current optimum powders too.
Now that I've done the 'invention description' I seem to recall having seen a scalloped bore before but don't remember where!