What is a “bore rider” bullet?

[RUFFIAN R - NY]

a buddy gave me a few of them 20mm loaded a few years back - was a HOG pilot, makes for a great conversation when compared to a 17 cal then up to a 50 BMG and then the 20mm. Just a little difference between them all. Never have fired one of the 20mm , would make a heck of a varmint gun !!!!

 

[MagnumManiac]

View attachment 365104

The above example is not a bore rider, that is a "Driving Band" projectile for a military multiple groove barrel.
It may be the concept behind a bore rider, but it's not the same at all.

Cheers.

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?

No, the amount of shank contacting the rifling has zero influence on twist rate, stability or terminal performance.
What it does do is change the pressure at which maximum is reached…without the bore rider section(s) the pressure would rise far faster and the velocity would be far less.
Removing friction by using a bore rider bullet, either as grooves cut into the shank, like a TSX, or using a far shorter shank at bullet diameter increases velocity without spiking pressure too soon.

Cheers.

 

[Dragoon300]

The above example is not a bore rider, that is a "Driving Band" projectile for a military multiple groove barrel.
It may be the concept behind a bore rider, but it's not the same at all.

Cheers.

No, the amount of shank contacting the rifling has zero influence on twist rate, stability or terminal performance.
What it does do is change the pressure at which maximum is reached…without the bore rider section(s) the pressure would rise far faster and the velocity would be far less.
Removing friction by using a bore rider bullet, either as grooves cut into the shank, like a TSX, or using a far shorter shank at bullet diameter increases velocity without spiking pressure too

The above example is not a bore rider, that is a "Driving Band" projectile for a military multiple groove barrel.
It may be the concept behind a bore rider, but it's not the same at all.

Cheers.

No, the amount of shank contacting the rifling has zero influence on twist rate, stability or terminal performance.
What it does do is change the pressure at which maximum is reached…without the bore rider section(s) the pressure would rise far faster and the velocity would be far less.
Removing friction by using a bore rider bullet, either as grooves cut into the shank, like a TSX, or using a far shorter shank at bullet diameter increases velocity without spiking pressure too soon.

Cheers.

It is most certainly a bore rider, as the diameter forward of the driving band, does ride on the bore. Yes it is steel to steel contact and it is going the projectile straight out the bore.

 

[Scott E Ames]

I know that my 45 cal. smokeless muzzleloader uses bore rider bullets. Same concept as regular driving band bullets.

 

[Coyote Shadow Tracker]

Just some comparison.
5.56 Ball & Tracer M-16A1 from Viet Nam
30 cal Carbine from WWII
338 LM, Current
.45 Ball cal - 1911 from WWII
20 Mike Mike Explosive head Navy from WWII (not sure how it was used, my father had it in his "BOX" from WWII along with the .45 and .30 never talked about it). The 5.56s and .338 are mine.

 

[FEENIX]

a buddy gave me a few of them 20mm loaded a few years back - was a HOG pilot, makes for a great conversation when compared to a 17 cal then up to a 50 BMG and then the 20mm. Just a little difference between them all. Never have fired one of the 20mm , would make a heck of a varmint gun !!!!

"If" by HOG pilot you mean WARTHOGS as in the A-10s, they use 30MM in their GAU-8 Gatling gun.