PRB flight question

[pepperbelly]

OK, it's time to expose more ignorance on my part. How does rifling affect a prb? I understand the stabilizing twist rifling imparts to my modern bullets, but does it stabilize a round projectile? If so, how?
I play softball and a pitcher who can throw a ball with no spin it tough to hit against. Is a prb equilavent to a knuckleball? If so how can they be as accurate as they are?
What happens to a ball from a smoothbore?
This has been keeping me up at night.
Thanks guys,
Jim

 

[roundball]

OK, it's time to expose more ignorance on my part. How does rifling affect a prb? I understand the stabilizing twist rifling imparts to my modern bullets, but does it stabilize a round projectile? If so, how?
I play softball and a pitcher who can throw a ball with no spin it tough to hit against. Is a prb equilavent to a knuckleball? If so how can they be as accurate as they are?
What happens to a ball from a smoothbore?
This has been keeping me up at night.
Thanks guys,
Jim

A RB from a smoothbore has no intentional rotation, like a knuckleball;

Rifling turns a RB like rifling turns a bullet...because a RB is round, it doesn't need as much spin since it's not an elongated projectile that needs to stabilize about a long axis.

:m2c:

 

[pepperbelly]

Thanks RB! I know that when I throw from 3rd to 1st I impart spin on the ball, and it goes straight (unless I throw a curve and hack off my 1st baseman). When warming up a teammate throws a knuckler once in a while. It moves all over.
A roundball needs less spin to stabilize. I know that backspin makes a softball fly further and topspin makes it dive. When I throw, I am righthanded, my ball tends to drift to my right because of a slight amount of sidespin.
When a prb is set spinning by the rifling does it tend to move to one side?
Jim

 

[roundball]

Thanks RB! I know that when I throw from 3rd to 1st I impart spin on the ball, and it goes straight (unless I throw a curve and hack off my 1st baseman). When warming up a teammate throws a knuckler once in a while. It moves all over.
A roundball needs less spin to stabilize. I know that backspin makes a softball fly further and topspin makes it dive. When I throw, I am righthanded, my ball tends to drift to my right because of a slight amount of sidespin.
When a prb is set spinning by the rifling does it tend to move to one side?
Jim

I don't think so but I'm no authority on it...I only say I don't think so because I've never heard or read anything in my life that suggests that's the case...maybe others know better.

ie: my .45's have right hand twist, my other's have left hand twist...they all sight in and shoot the same way

 

[Bob J]

When I throw, I am righthanded, my ball tends to drift to my right because of a slight amount of sidespin.
When a prb is set spinning by the rifling does it tend to move to one side?
Jim

According to an article in Muzzle Blasts, there is a theoretical drifting effect in the direction of the twist.

 

[pepperbelly]

Maybe the short range, under 150 yards, keeps it from becoming apparent.
Have any of you bore sighted your rifle? If the sights and bore are aligned there probably wouldn't be a drift, unless it is too small to notice until you go past 300 or 400 yards.
I gotta go see if I can find the ballistic coefficient of a roundball.
Jim

 

[Zonie]

Jim: "I gotta go see if I can find the ballistic coefficient of a roundball."
The Lyman Black Powder Handbook gives the following ballistic coefficients for round balls:
.310 dia=.043
.350 dia=.049
.440 dia=.062
.490 dia=.068
.495 dia=.070
.535 dia=.075
.570 dia=.080

Hope this helps.

 

[pepperbelly]

Thanks Zonie.
I visited Chuckhawk's site. There is an article saying that bc has no place in bp, but they were talking mainly conicals and sabots.
There was a very interesting article there stating that bc is not static, but changes with distance/velocity.
It really doesn't matter as long as I find a load my rifle likes, but I'm nosy about a lot of stuff like this.
Jim

 

[redwing]

You will notice what is refered to as (Yaw) at long range.
As the projectal slows down it tends to move off line or
drift in the direction of its rotation.

Redwing :redthumb:

 

[pepperbelly]

Does wind drift mask yaw?
Jim

 

[scott k]

One thing that a baseball and softball has that a prb doesn't have is threads and seams. The seams on a baseball effect the way it moves in the air.
a prb is spun by the rifing like a top to give it gyroscopic stability. :m2c:
Lehigh..

 

[Slamfire]

Does wind drift mask yaw?
Jim

It could well accentuate it or cancel it depends on the drift and the direction of the wind. There is also a drift imparted by the rotation of the earth, but is so weak muzzleloaders can safely ignore it. Artillery gunners can't though.

 

[robinghewitt]

Now I understood that the problem is that the ball isn't perfectly round, so it will offer different drag down one side which will pull it off course in a random fashion.

Spinning the ball means the side with the drag is pointing in all directions, so it spirals on to the target.

They set the flights on crossbow bolts to impart spin so they obviously understood the concept before they applied it to guns.

Another question is the ball with an off centre casting bubble inside. It spins concentric to the bore until it reaches the muzzle, when it will suddenly start to spin around it's centre of gravity. But does it side step? ::

 

The ball is also not perfectly round after being fired due to obturation (sp?). It's not quite a cylinder but leaning a tad in that direction.

 

[robinghewitt]

The ball is also not perfectly round after being fired due to obturation (sp?).

Are we allowed to discuss obturation here? After looking at the fizziks I think they go egg shaped, big end first :thumbsup:

 

[roundball]

........obturation (sp?).

:hmm:
I'm pretty sure that doesn't happen in any of my rifles...I've recovered .45/.50/.54cal balls from several deer...and also balls after being fired into a line of gallon water jugs...never had any that showed land and groove marks...surfaces are as smooth as when I loaded them

 

Obturation is a proven property on Minie's and slugs so are we postulating that a ball in a greased patch doesn't provide enough resistance to upset in front of a big powder charge? I'm not arguing - just asking for clarification. If the ball does exit as a perfect sphere, then defects like air pockets and sprues vestiges should impart very marked effects on its flight.

 

[roundball]

Obturation is a proven property on Minie's and slugs so are we postulating that a ball in a greased patch doesn't provide enough resistance to upset in front of a big powder charge? I'm not arguing - just asking for clarification. If the ball does exit as a perfect sphere, then defects like air pockets and sprues vestiges should impart very marked effects on its flight.

I wasn't arguing either...I simply shared the observation that I've never seen any evidence of land and groove marks on my recovered patched round balls...and I've always assumed that if obturation occured it would result in some sort of marks on a ball.

When I've run casual experiments at the range of shooting into jugs of water, or when I recover the occasional ball under the hide on the far side of a deer, there's a natural curiosity to inspect them closely...and they're always as smooth as silk...and that's using max and near max hunting loads...that's simply been my experience, that's all...they don't look any different than if I'd seated a ball, then blew the ball back out with compressed air.

Are you saying that you and/or other people who shoot round balls routinely find them with land and groove marks on them like a centerfile rifle or pistol bullet has?
:shocking:

 

[Rebel]

"they don't look any different than if I'd seated a ball, then blew the ball back out with compressed air."

Are you saying that your round balls don't flatten out when you fire them into something, or am i misunderstanding you?

 

I don't believe a roundball is accurate enough, far enough for drift to very obvious, but if it were accurate enough, far enough drift would become evident. Drift is the movement of a projectile in the direction of the rifling. Right hand rifling, right drift, left hand, vice/versa. Deflection of the projectile is caused by the wind. The two terms are often mis-used. Unless my memory fails me the drift of a 500 gr., 45 cal. bullet started at about 1100 fps, at 500 yards is approximately 20 inches. I can attest to that from the personal experience of having fired lots of rounds at 500 yards on dead calm days and having to adjust my rear sight to the left. I seem to remember that drift wasn't obvious until outside 300 yards. Slow twist round ball barrels probably wouldn't show as much drift as the common 1-20 twist of 45 cal. cartridge rifles but drift would assuredly be present.

I can't believe a roundball doesn't obturate to some degree but have precious little evidence to back up my belief. On the few round balls I've bothered to recover there were definite markings of the patching material being impressed upon a shank of the ball. I can't say if this occured at loading or upon firing. It just seems to me that the ignition of 70-120 grs. of black powder behind a soft lead projectile would have to cause some obturation. Lighter charges in cartridge rifles certainly obturate the bullets, and yes, I understand the difference in the weight and resistance offered by a 500 gr., 45 cal. bullet as compared to a 130 gr. PRB. Those are my thoughts.

Vic