Roundball Sprue Orientation

[Ironwood]

If you cast or use cast roundballs, how do you orient the sprue or nib of the ball when you load? Up? Down? Not concerned?
 
Also whose mold are you using?
 
As for myself I cast a .490 roundball with a Lee mold. I'm not concerned with where the sprue is when I load. I do most of my shooting at 50 yards and I haven't noticed any problems with accuracy. If the first shot goes where I aim, and the next two go within an inch or so of that one, I'm happy!:)

[quigleysharps4570]

Sprue up is how I've always placed them. My roundball moulds are Lee .44's, .50's and .54's.

[Alboy]

I was taught to sprue up and have just never done it any other way. Exception being RB's from Hornady that were store bought, no sprue mark was noticeable. Some of those were dimpled like golf balls from riding in that box for a small eternity, did not seem to affect my accuracy to any great extent.

[gitano]

Now I'm gonna join in this discussion acknowledging right up front that the summed total of my ML RB shooting experience is half a dozen or so when I attended the State's qualifying course. However, as most of you well know, I'm not usually without an opinion on ballistic matters. Here are my thoughts:
 
I think I understand why it is recommended by many that the sprue should go "up". When firing non-roundball projectiles (jacketed and cast bullets), it is fairly well established that small perturbations to the base of the bullet make big differences in precision. This is explained by pointing out that inconsistencies in the shape and diameter of the base of the bullet cause the propelling gasses to exert unconsistent pressure on the base of the bullet as it passes out of the muzzle. Of course, if gasses are pressing harder on one side of the base of a bullet as it exits the muzzle, the bullet is going to be 'tipped' to one side or another... and of course that's not exactly "good" for precision. However, I think the significant feature of a bullet, with regard to this subject anyway, is the fact that it is essentially a cylinder. The importance of that is that with a cylinder, "inconsistencies" in its base are going to manifest themselves at the edge. The roundball, I think, is different.
 
Compared to a cylindrical bullet, the RB has precious little bearing surface in contact with the bore. With the sprue "up" OR "down", the bearing surface of the RB is unaffected as it exits the bbl. If, on the other hand, the sprue were oriented to the "side" such that it was part of the bearing surface, inconsistencies in bearing-surface-contact would certainly occurr, and precision would just as certainly degrade. What about downrange flight after the RB has left the muzzle?
 
Well, I suspect that a "nasty" sprue would have some effect on in-flight trajectory, but I doubt if it would be more than putting that same "nasty" sprue in the "front" of the bullet's flight.
 
All in all, due to my almost non-existant firsthand experience, I'm purely speculating here, trying to figure out the causes of why "sprue up" or "sprue down" might make a difference in precision. Personally, I think the most important "method" to practice is consistency. Always "up", or always "down", seems more important to me than whether "up" or "down". But again, I'm not experienced enough to even qualify as a novice.
 
Paul

[Stryker]

I was taught Sprue-up. Grandpa said if the sprue was down or off to the side, you risk tearing the patch. A torn patch will cause more grief than the ballistic coefficient of a round projectile.

[Ironwood]

Stryker... You don't have to worry about the ball tearing the patch. Actually the cotton patch is harder than the pure lead ball. Yeah I know, took awhile for it to sink in with me also. :)
 

 
See how the cotton patch pushed into (engraved) the lead ball instead of the other way around. From what I've read that patch isn't thick enough. The patch should lightly engrave where the grooves are also, not just the lands.

[Stryker]

I would agree with you about cotton pillow ticking. Granpa used whatever was available usually muslin, which while cotton, is a more sheer material and ripped much easier then ticking. I shot muslin and onasburg for quite a few years until I went to a slightly undersized ball. Now I use pillow ticking or lightweight denim.

[Jay Edward (deceased)]

Now I'm gonna join in this discussion acknowledging right up front that the summed total of my ML RB shooting experience is half a dozen or so when I attended the State's qualifying course. However, as most of you well know, I'm not usually without an opinion on ballistic matters.

OK... I like the logical approach you've taken.  Now, what I want you to comment upon is the effect of the existence (or non-existence in the case of the Lee) of a snall lead weight (sprue) on the rotation of the ball over an extended range.

Then I want you to compare the likely accuracy of a perfectly roundball compared to a roundball that is, in essence, 'out of round'.

The range we will be speaking of is at least 100 yards as even a smoothbore can shoot a pretty straight ball to 50 yards.
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[Alboy]

I have an opinion but i want to see the number cruncher go first. Not a simple question Jay but not too bad. Remember the simpler the better as it drives him into tizzies.

[Ironwood]

Jay, I'm not going to be shooting at anything with a roundball at 100 yards.

[gitano]

Now, what I want you to comment upon is the effect of the existence (or non-existence in the case of the Lee) of a snall lead weight (sprue) on the rotation of the ball over an extended range.
 
Then I want you to compare the likely accuracy of a perfectly roundball compared to a roundball that is, in essence, 'out of round'.

Hmmmm..... OK, I'll bite.
 
I see your point regarding 'ballance'. Considering ballance, I'm inclined to think the weight-forward (sprue "up") condition might be the best, but only if it was perfectly centered on the axis of rotation and not particularly "ragged". Here's my rationale:
 
What is "True" is that projectiles "prefer" to travel with their center of mass at, or forward of their center of form. This is proven every time a bullet "tumbles" while inside its target. The infamous "terribly destructive" M-16 .223 bullets come to mind here. They were supposedly "designed" to tumble when they hit a person. The fact is, everything wants to travel weight-forward. So, if the sprue "up" orientation moves the center of mass forward of the center of form, the RB should 'prefer' to maintain that orientation and therefore be more stable.
 
In the sprue "down" orientation, the center of mass is aft of the center of form. Therefore, at some point down range, the RB is gonna wanna "swap ends". In doing so, it will 'destabilize', at least to some degree. Being a round ball the effect of "swapping ends" is substantially less dramatic that it is for a long, cylindrical bullet. HOWEVER...
 
It also occurrs to me that with the sprue "up", AND NOT perfectly aligned with the axis of rotation, the RB will 'wobble', and if it should 'catch an edge' of the 'ragged' sprue, the wind resistance will also cause it to 'swap ends'. In that case, to the opposite configuration it 'prefers' - namely CoM aft of CoF. Therefore, theoretically at least, it should 'want' to swap ends back again to return the CoM to a point ahead of the CoF. And then 'catch an edge' again... and then move the CoM back in front of the CoF... and then... and then... Seems unstable to me.
 
So, still ignorant of what happens "in real life", I come back to consistancy as the best plan.
 
OK Boss... what say you?
 
Paul

[Jay Edward (deceased)]

OK Boss... what say you? Paul

I say we buy moulds that leave a slight sprue extension, trim off the sprue to conform as closely as possible to the radius of the roundball, weigh the pure lead ball to eliminate those with internal air spaces, put the balls between two extremely flat surfaces (such as plate glass), roll them back & forth until we are sure they are as concentric as we can make them and try some 100 yard shooting.

I respect the fact that Ironwood has no intention of shooting at 100 yards but I really feel that, if I were able to get him to within 150 yards of a Boone & Crockett bull Elk, he would be mightily tempted to take the shot on the Elk.



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[Ironwood]

Jay, You might be tempted to shoot at a elk at 150 yards with a patched 177 grain roundball, but ol' Ironwood wouldn't.  I know my limitations and have to much respect for the elk to even think about doing such a thing.  If I were hunting elk I wouldn't be using a roundball to start with.  :)

[Smokepole]

Okay, now it is time for the rocket-scientist to throw a monkey wrench into the works.
 
I look at the sprue up/down/sideways like a bowling ball. Before a bowling ball is drilled with holes, it is placed on a "doo-doo" scale. This scale can measure the imbalance on all six sides of the ball, left/right, top/bottom, front/back. The amount and position of the imbalance determines not only the axis rotation but also the degree and direction of "curve/hook".
 
As the ball is released by the bowler, he imparts an axial rotation to the ball. When the ball is projected and rotates down the lane, the ball will attempt to stabilize its rotation about its natural axis. Due to CoF between the lane and the ball surface, the ball tends to slow its forward projection. The imbalanced drilled into the bowling ball determines the length of travel and the amount of "hook" or direction change (Rg, Differential). This imbalance is only in the amounts less than 1 oz. with respect to its opposite side. If there are changes in forward ball speed, the reaction will be different.
 
This was demonstrated with a gyroscope. The gyro was spun-up and it will find its horizontal axis of rotation. When 1/8 oz of weight was applied to right side of the rotational axis, everyone thought the gyro would tend to tilt in that direction. However, the gyro actually rotates about its vertical axis in a counter-clockwise direction. Now a new vector direction has been imparted to the object causing a new direction.
 
Granted a bowling ball is generally traveling at 18 – 20 M.P.H. with a rate of spin of about 300 – 350 r.p.m. much slower than the round ball, but I would think the maybe the same principles would apply.
 
I believe this could be similar to the reaction of a round ball as it leaves the barrel. Lands and groves create the rotation, powder charge the velocity or forward projection. The ball will try to establish its own axis of rotation based on the position of the sprue. As we all know, the ball is slowing and loosing energy as it travels down range. As the velocity changes, the effect of the sprue could play a major part in the "flier", just as the imbalance in the bowling ball.
 

All of this would leave me to believe the need for consistency in our loading practices.
 
I've included the calculations for "rate of spin" for the round ball.
Whether roundball or conical, any bullet fired from a rifled barrel spins as it travels to the target. Spin is responsible for stability in flight, a very important factor in accuracy. Think of a ball fired at 2000 fps from a barrel with 1:66 twists. To calculate spin, assume the bullet will travel a distance equal to the velocity, e.g.: a ball at 2000 fps will travel 1 full second and go 2000 feet. Then, convert twist rate to feet, so that 1:66 = 66 divided by 12 in. = 5.5 feet. If the ball travels 2000 feet in one second, and spins around once every 5.5 feet, it will spin 2000 divided by 5.5, or 363.63 times in one second, rps. We then convert to rpm by multiplying rps by 60, so 363.63 x 60 equals 21,818 rpm.

 
An elongated bullet flying through the air without spinning will be unstable and inaccurate. The longer the bullet is in relation to its diameter, the more spin is required to stabilize it. How much spin is required? This relationship is expressed in the Greenhill formula, a simplified verson of which is:
 
150 x diameter squared divided by bullet length = required spin
 
Example for a .45 caliber bullet .60 inches long:
 
150 x .45 x .45 divided by .60 = 50.6 inches
 
So, for the example bullet, a spin rate of 1:50.6 or faster is required
 
The formula can also provide us with the maximum bullet length which can be stabilized by a given barrel twist. The formula becomes:
 
150 x diameter squared divided by twist rate
 
Example for a .50 caliber barrel of 1:48 twist:
 
150 x .50 x .50 divided by 48 = .78 inches
 
The barrel will stabilize a bullet .78 inches long, or shorter.

 
 
Now is everyone confused.
 
 

Smokepole

[gitano]

I say we buy moulds that leave a slight sprue extension, trim off the sprue to conform as closely as possible to the radius of the roundball, weigh the pure lead ball to eliminate those with internal air spaces, put the balls between two extremely flat surfaces (such as plate glass), roll them back & forth until we are sure they are as concentric as we can make them and try some 100 yard shooting.

I see.
 
Shoulda known there was an easy solution. :D
 
I can see the sprue trimming, but the glass plate thing seems like it could cause out-of-round just as easily as it could round a ball. I'd stop with the sprue-trimming 'til I could get training on the glass plate technique.
 
Paul[/color]