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Why is it that round lead ball ammo generally performs poorly in AGs?

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G

greg

Member
Apr 2, 2015
172
11
Washington
This more of a theoretical question, but really, what's wrong with a perfectly round ball as a projectile? The weight seem to be quite respectable, e.g. in .22 its around 15-16gr, and making balls on the industrial scale also ought to be less tricky than a diablo shape.

I understand that the lack of a skirt will prevent a round ball from creating a good seal, and if there are dents/nicks - those will surely affect precision, but assuming a very high quality lead ball can be made (which is likely to be the case, after all we've mastered precision ball bearing manufacturing), what other factors do you know that contribute to round ball's poor performance?
 
Within a few calibers after it emerges from the barrel it is then initially flying at 500 to 600 miles per hour. Any discrepancy in rifling imprints then become an unbalancing force in that airflow. Any fractional loss of precise frontal presentation would then show engraved rifling on one aspect to the oncoming air stream but smooth "head" surface on the opposite aspect. We then have the precursor to a whoopsy doodle. ... I think. 

Perfect rifling and such as would also not leave unsymmetrical trailing foil just may get us what we should like if the pellet too was perfect. ... Kind regards, Harry.
 
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Thanks for the thoughts, guys. I agree with what's been said.

To continue on what Harry and Aaron suggested, I guess the round shape dictates a very small surface area for a rifling (or smooth twist) to grab on, thus less of a spin to begin with, probably. Adding an insult to injury is also the fact that as far as gyros go, the further the spinning mass is from the rotation axis - the stronger is the gyroscoping effect (aka stability, e.g. a partially hollow diablo pellet has a lot more mass away from the center)
So, slower initial spin plus poor stabilization means the ball is liable for precession and even out right tumble in flight, which should inevitably result in 'woopsy doodle' as Harry so eloquently put (is it a Latin term?).

Still, I got a tin of round balls just for kicks and will report back when I get a chance to try them out from my .22 ST barrel :)
 
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And Then....
You have the anomaly where as round ball out shoots any other type of projectile ran through the air gun....
For instance, I have an Evanix Max ML in .45. Evanix list the barrel as having a .453 bore diameter, and a barrel that has 16 grooves with 1:15 right-hand twist.
.454 size round ball at 140gr punches nice tight groups at 50 yards, barely holding still.......
the 3 pictures are of 3 shot groups with the aforementioned RB, (first 2), and of .122 grain cast bullet...while both groups are pretty good IMO, the RB is repeatable group after group.

DJ












 
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The ball to bore fit is much more important in an airgun. With black powder or smokeless powder firearm the ball will actually squish to bore size. However, even the highest pressured airguns are pipsqueaks in comparison. The low pressure shotgun loadings, for example, run in the 10,000 + psi range. When you get into BP rifles, the pressure goes to around 30,000 psi. 

The twist rate on most airguns is plenty fast enough to stabilize a round ball. In theory, but not practice, a round ball needs no twist. However, imperfections will allow a non-spinning round ball to take on a random spin and will behave like a knuckle ball in baseball.

With the round ball, it needs to fit the groove diameter exactly or with just a slight interference. Too much of an interference fit can cause unwanted distortions. 
 
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"ztirffritz"I often wondered why round balls weren't made with dimples, like a golf ball. It is supposed to stabilize the ball in flight and help it travel faster and farther.
Click to expand...
The golf ball spins 90 degrees to the way a bullet spins. The dimples do two things: they first give a bit of bite to the air which further reduces the air pressure along the top side, and second they create vorticies which reduce the skin drag effects. 

However, I played with this idea using both round balls and Crosman Premier Heavies. I used 60 grit glass bead blasting media. I glued a thin layer of media onto a flat piece of steel. I rolled a sample (30) of round balls, and the noses of CPHs on the plate until there was an even dimpling. 

I found, though, with the round balls and the CPHs there was a slight increase in drag. I shot samples with chronograph screens at 2 and 27 yards with untreated and treated projectiles. The 2 yard screens showed no significant velocity difference, however the treated projectiles showed slightly lower velocities at 27 yards. The other thing that happened was there was more spin drift noticed at the 30 yard target. Groups were larger as well.

Unfortunately, dimples on projectiles rotating about their axis of travel, do not seem to reduce drag, and do not seem to increase the accuracy/precision. The evidence by this one trial seems to indicate the opposite to be the case. 
 
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Circling back to report on a quick experiment I did with 15.4 gr .22 Gamo Round ball ammo in my FX Indy.In short - no (pleasant) surprises.The ammo itself was unbelievably dirty and greasy, so I washed it thoroughly before testing.

1. The shape of the RBs was very rough. There were large pits and crevices on most of them.
2. Diameters were very inconsistent, the same ball could read as much as .3 mm off depending on where the calipers were positioned
3. Weights were quite inconsistent as well, as much as .6 grain difference in a random sample of about 40 pellets weighed.
4. No wonder that all of the above resulted in ridiculous chrony results. On power setting 2 (~650 FPS, 16 FPE) I was getting extreme spread of 60 FPS over 6 shots! I was shooting in a known plateau pressure range, which for JSBs 15.9s, for example, produce reliable strings under 10FPS extreme spread.

Obviously, no point in trying to shoot this for accuracy even at short range :) 

(edit: formatting)
 
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Round ball work great in airgun that have the right barrel. Faster than 1:20 twist they do not seem to work in as well and choked barrel is probably not a good choice. However, in slug shooting guns round ball shoots more accurately than a lot of bullets people shoot out of their airguns.

There is also two ways to make round ball. One is to cast it and the other is to swage it. Cast are not nearly as good nor nearly as accurate because they have a flat spot from cutting the sprue. Swaged round ball are much better and have no flat spot so they are perfectly round. Hornady and Speer make the best round ball which is swaged and good, cheap plinking ammo.

Slower twist rates work best with round ball. In my Texan we get about 2-2.5" inch groups at 100 yards with round ball on a good day. We have bullets that do better but that is not bad for a simple round ball. I make another round that is 168 grains (round ball is 143) that has better ballistics and a better shape for hunting which is more accurate and works great in Texan and Sam Yang 909 or Evanix 45's.
 
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