[Crosshairs10]

Given that two identical .58 caliber muzzleloaders are fired by shooters standing on the same firing line simultaneously, from the same height.

(Assume that both are percussive and equally loaded. One is a smoothbore and the other is rifled.)

Which round ball has the greater muzzle velocity?


Thank You

 

[unclenick]

Assuming a good bore seal to prevent gas bypass from both barrels, a fast enough powder may favor the smooth bore if the mass of the projectile is high enough that the powder all burns before the bullet can move significantly. But for progressive powders or powders that are a little slower it can go the other way. The smooth bore has less friction. I know from experience that when you moly-coat bullets you tend to lose 50 fps or so in rifles because the slick bullet doesn't offer as much resistance for the powder to build pressure against. The energy transfer becomes less efficient and you have to increase the charge a little bit to get back to the same velocity (usually 1% or so).

The answer to question 2 is the one in the rifled barrel. Balls in smooth bores tend to roll a little. Any kind of spin not on an axis perpendicular to the trajectory can pull the ball off track by the differential in pressure that creates. Same as a curve ball.

 

[Crosshairs10]

Assuming a good bore seal to prevent gas bypass from both barrels, a fast enough powder may favor the smooth bore if the mass of the projectile is high enough that the powder all burns before the bullet can move significantly. But for progressive powders or powders that are a little slower it can go the other way. The smooth bore has less friction. I know from experience that when you moly-coat bullets you tend to lose 50 fps or so in rifles because the slick bullet doesn't offer as much resistance for the powder to build pressure against. The energy transfer becomes less efficient.

The answer to question 2 is the one in the rifled barrel. Balls in smooth bores tend to roll a little. Any kind of spin not on an axis perpendicular to the trajectory can pull the ball off track by the differential in pressure that creates. Same as a curve ball.

Thanks Unclenick!

 

[Crosshairs10]

The Magnus Effect

Trying to Resolve an old Civil War problem I am having with smoothbores versus rifled bores:

The Magnus Effect is described as a perpendicular force experienced by a projectile, spinning in at a 90 degree angle to direction of projectile's flight. This spinning in one direction increases the pressure on the opposite side of the direction of spin, causing the sphere to be forced to move into the direction of spin. The magnus effect is usually offset by the gyroscopic spin.

Based upon this description, shouldn't a rifled round ball shot from a muzzleloader be more subject to this phenomenon than a round ball shot from a smoothbore?

If this assumption is true:

Why wouldn't a round ball from a smoothbore have greater range, since it's less subjected to this phenomenon?


* Assuming range is linear for all practical purposes.

 

[unclenick]

That's the same thing I described as the curve ball effect. The Wikipedia has a nice illustration, here. The only spin the ball can have that won't pull the ball off course to a curving trajectory is spin perpendicular to the trajectory. That's because spin in that direction doesn't alter oncoming air speed or circulate air over the ball surface on one side more than the other to create a pressure differential. Rifling starts the ball out of the muzzle spinning in that non-influencing direction, perpendicular to the trajectory, and gyroscopically discourages it from picking up spin on some other axis that would cause the trajectory to curve.

 

[crazydave]

That's the same thing I described as the curve ball effect. The Wikipedia has a nice illustration, here. The only spin the ball can have that won't pull the ball off course to a curving trajectory is spin perpendicular to the trajectory. That's because spin in that direction doesn't alter oncoming air speed or circulate air over the ball surface on one side more than the other to create a pressure differential. Rifling starts the ball out of the muzzle spinning in that non-influencing direction, perpendicular to the trajectory, and gyroscopically discourages it from picking up spin on some other axis that would cause the trajectory to curve.

Excellent response!

I'd also note the averaging effect on the center-of-mass and suface features' wind resistence dealing with slightly imperfect projectiles in the SLOW spin of roundball barrels....

 

[unclenick]

That averaging actually happens with all projectiles if the spin is adequate to stabilize them, whatever that spin rate happens to be. A round ball is a special case for a a couple of reasons, but the end result is that spinning it makes it shoot better. That it lacks the overturning moment of an elongated projectile allows that spin to be much slower than it must be for a long shape.

 

[ribbonstone2]

Even if the barrel doesn't induce some kind of spin (and with a tight patched round ball, it's not likely to pick up barrel spring), it's going to pick it up somewhere along it's path from tiny irregularities.

Basically, even if you throw a perfect knuckle ball, it's going to pick up a random spin.

But if you could, and everything else was "perfect", would bet on the smooth bore being faster. SApinning a bullet takes energy, and that energy has to come from the powder charge.

 

[jwp475]

Takes very little effort to impart spin and as Uncle Nick stated if one reduces the friction the pressure is also reduced and so is the velocity

 

[unclenick]

I think I did the spin calc in another thread recently. Without looking it up, for high power rifle it seems to me it was equivalent to stealing one foot per second or something like that off the peak velocity. Much smaller than my intuition suggested.

The random flap of the butterfly wing is definitely right, though. The group error is a pretty typical bell curve on each coordinate axis. And without a patch it's usually much worse.

 

[mikmarandola]

Thank you now I Know another reason a brown bess was so inaccurate apart from the excessive windage of sub caliber balls. I know a curve ball is a baseball thing and that it could be thrown deliberately. I love it when I can say "now I understand."

 

[BAGTIC]

Everything is imperfect to a greater or lesser degree. Perfection only exists in the abstract. With a spherical projectile as long as it stays spherical spin is not needed to stabilize it. The spin exists to regulate the unintentional irregularities of both form and trajectory. It is the same reason drag stabilized projectiles such as rockets, fin stabilized artillery projectiles, and arrows are designed to slowly rotate, It is not to stabilize them. It is so the direction of the errant forces constantly change vectors so as to avoid the effects of those forces accumulating in a single direction thereby cancelling out the effects.