The bullet has a section near the base at full bullet true diameter, then the rest of the shank is at bore diameter generally.!!!!!!!!!!!!!!!!!!!There have been many cup and core "bore rider" bullets. The original Winchester design of the 264WM used a bore rider bullet to reduce pressure and keep velocity up. It didn't match the advertised velocity, but was faster than a full shanked bullet.
The bullet has a section near the base at full bullet true diameter, then the rest of the shank is at bore diameter generally.
Cheers.
Perfect size for tree rats
OO-OOF!! Hate to be on the receiving end of that!! 20mm??
Yes - 20mmOO-OOF!! Hate to be on the receiving end of that!! 20mm??
No, the projectile length to diameter is the primary factor. The bore rider design reduces friction, especially on longer projectiles. They are often used in conjunction with gain twist rifling to help get heavier projectiles turning easier. Like in the 20 mm Vulcan with the projectile posted above, the rifling starts pretty much straight at the beginning and ends up twisted like a cork screw to spin it fast enough to stabilize. The bore rider also gets the projectile aligned in the bore prior to firing, unlike standard bullets.Am I correct in thinking that bearing surface area is one of the factors in determining ideal barrel twist for a given projectile? And if that is correct, then what is the ideal twist for a "bore-rider" where only a short section of the projectile is engaged in the rifling?