05-28-2015, 11:21 PM
I have been told that the polygonal barrel can get mildly increased velocities without the accompanying increase in peak pressure.
The idea is that the polygonal rifling decreases the engraving force which slows the initial pressure buildup. The bullet to bore seal is said to be better with the polygonal rifling compared to the relatively sharp transitions from land to groove and vice versa. The notion is that a better gas seal keeps more gas available for doing work on the bullet so the pressure does not fall off as quickly.
The net result is that powders appear to burn a bit slower, which allows a bit more charge, further increasing the effect.
NugginFutz may have more on this.
In my view, the case for this set of effects is yet to be made in a technically substantiated way, but I am hoping one of us has links to a definitive and experimentally supported paper.
The idea is that the polygonal rifling decreases the engraving force which slows the initial pressure buildup. The bullet to bore seal is said to be better with the polygonal rifling compared to the relatively sharp transitions from land to groove and vice versa. The notion is that a better gas seal keeps more gas available for doing work on the bullet so the pressure does not fall off as quickly.
The net result is that powders appear to burn a bit slower, which allows a bit more charge, further increasing the effect.
NugginFutz may have more on this.
In my view, the case for this set of effects is yet to be made in a technically substantiated way, but I am hoping one of us has links to a definitive and experimentally supported paper.