Smoothbore rate of twist?

[Gun Tramp]

The .672 balls on the right were recovered from soft wood, left one is unfired. The fired examples were loaded sprue cut-off up (forward) using both ends of the short starter for a nice square start, but show the sprue cut-off facing almost rearward at impact only fifty feet away. Target load, 60 gr. Fg and lubed .010 patch in .691 bore. I had assumed that there was inevitably a spin imparted to the ball in a smoothbore but here it is "tumbling" rather than the spin I expected. Have others noticed this?

 

[Jakeytoo]

I had assumed that there was inevitably a spin imparted to the ball in a smoothbore

Nope, no spin because it is smooth bored meaning no rifling to impart spin.

 

[leadhoarder]

I am sure it spins or tumbles a little bit once it leaves the bore. But the bore is not imparting it.

 

[Gun Tramp]

But the bore is not imparting it.

I don't know that; the recovered slugs only demonstrate that they did not travel as a knuckleball. I'd wager that someone at some point has studied this at length...

 

[Brokennock]

They turn around from air turbulence so the sprue, which doesn't cut through air as nicely as the smooth curve opposite it, travels in the rear.
Besides, rifling imparted spin would not be spinning the ball so that the ball spun along its front to back axis changing which side faced forward.

 

[George]

I had assumed that there was inevitably a spin imparted to the ball in a smoothbore,,,,

Why would you think there would be spin imparted to the ball in a smoothbore? What would be the mechanism?

Spence

 

[Sudsy]

How could it not be a knuckleball
Have you ever had a really big guy smash a knuckleballing line drive at you? I'd think it would be the same thing out of a smoothbore.

 

[BuffaloSoldier]

Why would you think there would be spin imparted to the ball in a smoothbore? What would be the mechanism?

Spence

Hello, from Missouri, just wondering? I'm a Spence, originally from Oklahoma.

 

[Phil Coffins]

I told the wife about the title of this thread, she laughed too!

 

[Bon Sauvage]

I don't know that; the recovered slugs only demonstrate that they did not travel as a knuckleball. I'd wager that someone at some point has studied this at length...

And I am NOT that someone. But as the ball bounced down the barrel it looks to me that it might have exited the muzzle at the top of a bounce or the bottom of a bounce and the escaping gases, under or above the ball respectively, caused a slight spin on the Y axis. It is still a slight spin only on a different axis than you were expecting.

 

[SDSmlf]

I have noted no predicable or repeatable spin on smoothbore shot roundballs. More like like a poorly thrown knuckleball at times with some some occasional decent movement. Predictable, but only with an ever increasing ‘bullseye’ as the distance increases. Takes a lot of practice to understand and take advantage of that ‘bullseye’ accuracy.

 

[George]

Hello, from Missouri, just wondering? I'm a Spence, originally from Oklahoma.

Hello, Spence from Missouri. I'm a Spencer from Kentucky, Spence is just a nickname. I inherited it from my Dad.

Spence

 

[Art Caputo]

Perhaps this explanation of the “Magnus” effect might explain the OP observing the change in the sprue position in the recovered round ball. Imparting a controlled spin to the object(ie. a rifled barrel) greatly reduces the effect, and variability of directional travel.

 

[Gun Tramp]

Why would you think there would be spin imparted to the ball in a smoothbore?

Because other smoothbore enthusiasts have said so. Thus my reason to recover fired projectiles and see for myself.

I have noted no predicable or repeatable spin on smoothbore shot roundballs. More like like a poorly thrown knuckleball at times with some some occasional decent movement.

I'm of the "poorly thrown knuckleball" camp, so I practice throwing the knuckleball poorly the same each time.

Perhaps this explanation of the “Magnus” effect might explain the OP observing the change in the sprue position in the recovered round ball.

Thank you, Art.

 

[George]

The Magnus effect occurs only when the projectile is spinning, doesn't happen with a smoothbore.

I'm not a believer in the "knuckleball" nonsense because my experience is that I can shoot accurately at long distance with my smoothbore. I have never seen the mythical change in direction at 50-60 yards which is so popular.

I think the shooter is the problem.

Spence

 

[Jakeytoo]

Because other smoothbore enthusiasts have said so.

I am a smoothbore shooter and disagree. Maybe a poll is in order.

 

[Sudsy]

For the non-smoothbore shooting guys following this thread.... At 75 yards what is considered a tight group, 2"... 8" ??

 

[Loyalist Dave]

Well first, the sprue projects from the sphere, so yes that might turn the ball as it travels. For it to "spin" in any manner it must make at least one Full revolution before impact OR it has merely turned.

How does one know if it turned during flight or actually spun, OR it turned due to friction on impact ? Anybody got a high speed camera we could use ???

LD

 

[David Veale]

it seems to me that there is undoubtedly some spin to a roundball fired from a smoothbore, and that this spin will affect the roundball's trajectory in a more or less random manner that becomes more pronounced with increased range. This is precisely why smoothbores do not have the accuracy of rifles. As someone stated above, it may be that the ball is "bouncing" down the barrel, or that imperfections of the ball surface (sprue, casting defects, etc) will create spin upon hitting the air outside the barrel.

The the whole point of rifling in that it imparts a predictable spin rotating around the axis of travel, and that the rotational inertia of this spinning overcomes the other effects of the sprue or barrel friction to give a predictable spin. A rifle's roundball may very well be drifting away from the line of sight (beyond the effects of gravity), but because it does so *consistently* each time, it can be compensated for with sight adjustment

 

[Britsmoothy]

The answer is simple.
Get the smoothbore straight rifled.
Or alternatively, shoot lots of steel shot through it.
That'll stop any random influence from the barrel