by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- Smoothbore Diana 25
- The $100 PCP
- The best article
- Smoothbore rifle
- Birth of the smoothbore rifle
- The results
- All balls spin in flight
- What have I just said?
I don’t like to use myself or this blog as an authoritative source, but when I research shooting round balls at high speed I find that I have written more on the subject than any other source. Or maybe not more so much as more that has been verified.
Smoothbore Diana 25
To get you started, read this 5-part report on the Diana model 25 smoothbore. Reading that you will discover several things. First, that smoothbore airguns are accurate out to 10 meters when shooting pellets. Next — it takes the right loading technique to shoot a pellet accurately from that airgun at 10 meters. We also learned that the same gun fell apart when the range was increased to 25 yards and shot the same pellets that were accurate at 10 meters. Finally we saw that round balls in this gun were not accurate at all.
The $100 PCP
Next, you will find that I experimented with both pellets and BBs in the 6-part series on the $100 PCP. If you look at the velocity data for BBs that’s in Part 2 you will see that we got BBs up over 800 f.p.s. with some consistency when the gun was filled to 2,000 psi.
The best article
The best and most germane report I did on this subject was written way back in 2012. It was titled Round ball accuracy in smoothbores. In that report I addressed the idea of shooting round balls in muzzle loading smoothbores, where they can produce a muzzle velocity in excess of 1,400 f.p.s., if they are loaded for it. Between that, which we didn’t do and the smoothbore BB-shooting PCP that we did try, we have looked at round ball accuracy at higher speeds. I will address that subject now.
The title sounds like a contradiction, but don’t dismiss it. Smoothbore rifles exist — or they did. Around the middle of the 19th century a group of midwestern shooters decided to see how accurate a smoothbore can be when it shoots a round ball.
A smoothbore rifle was either made that way from the beginning, or it was once a rifle that someone reamed the rifling out of to make the barrel smooth. Since the newest of these guns are more than a century old it is next to impossible to tell which it was.
Smoothbore rifles have fine rifle sights, while smoothbore muskets may only have rudimentary sights and fowlers (ancient shotguns) might only have a bead at the front to align the bore. While we think of shotguns shooting birds on the wing today, that wasn’t always the case. Old-time fowlers were often shot at birds roosting in trees or floating on the water. So they did need to be aligned with the target, but not aimed in the conventional sense.
Very few writers really understand what a smoothbore rifle is. They think it’s used for hunting and they talk of “buck and ball” which is a load of buckshot (large lead shot) over a single bore-sized ball. That was a popular hunting load for game like deer at ranges os less than 50 yards. It is not a smoothbore rifle load, though.
I have seen a real smoothbore muzzle loading rifle — one that was either made that way intentionally or converted from a target rifle. The barrel was made by Remington and measured 1-7/8-inches across the flats of its octagonal barrel. The percussion gun weighed about 15 pounds and was made for one purpose — to shoot round lead balls into the tightest group possible at a range of about 50 yards. Lest you think someone must be anal to do that for fun, I remind you that several of our own blog readers tether a carbon fiber air tank to a PCP to shoot it from a benchrest. Anal is as anal does.
Birth of the smoothbore rifle
From my reading in sources that are as rare and hard to find as some antique guns, I learned that in Ohio around 1850 a group of men started shooting smoothbores at targets to see how accurate they could possibly be. They soon learned that the fit of the ball to the bore was very important, but there was more to it than just that. The fit of the patch to the ball and bore was also very important. The best results came from patches of dense material like pillow ticking that were actually slightly larger than the bore of the gun when wrapped around the ball.
Here’s how it works. Say the bore is 0.50-inches in diameter — it would probably shoot a 0.490-inch ball. The normal patch would be a thin one because there is just 0.010-inches of free space between the bore and ball, and that includes both sides of the ball (a ball is a sphere, so every point on one side has a point on the opposite “side”). The patch material for this ball needs to be 0.005-inches in diameter for the ball to fit snug, but you can forget that. You won’t find good patch material that’s as thin as that. Maybe parchment would work and I’m sure they tried it, but the little that’s written about them indicates they used cloth patches.
A good tough cloth patch of pillow ticking will measure 0.015 inches thick. That means it will add 0.030-inches to the ball size, which is slightly too much. You would have to fit 0.30-inches into a space that’s 0.010-inches wide. That would require 0.020-inches of compression, which is too much to allow smooth loading. The ball would probably be deformed if it was rammed down the bore against that much resistance.
That leaves you with a couple options. Use a smaller ball or use a thinner patch. Or, do both. If those guys back then were anything like us, you know they did both things and probably a lot of other stuff besides.
I have read that they shot at lot at 50 yards because much farther and their accuracy started breaking up. That sounds like the results I was getting with the $100 PCP, doesn’t it? I got good groups at 10 meters and horrible groups at 25 yards.
What that leads to is my prediction that the Daisy 499 will not shoot at tight at 10 meters as the Haenel model 310 ball shooter, since the Haenel is rifled. That’s just a prediction. I have not done the test yet. But if that is correct it tells us that exploring the accuracy of a round ball at any distance is probably not going to end well.
All balls spin in flight
Reader GunFun1 said in a comment that he didn’t think a ball had to spin to be accurate. I don’t know if that is correct or not because, short of a high-speed slow motion camera, there is no good way to test it. Like it or not all balls in flight spin a little. When fired from a BB gun they spin from contact with the walls of the shot tube on their way out. That means the Red Ryder BBs all spin, and so do the BBs shot from a 499. So here is a question — if both guns have a smooth bore, why are the BBs shot from a 499 so much more accurate than Red Ryder BBs? I think the answer is the consistency of spin.
Consistency of spin means that all BBs spin the same way, and at nearly the same RPM. You get that kind of consistency (I think) when the shot tube bore is very close to the diameter of the BB. I can’t prove that but I can and have proven that Avanti Precision Ground Shot is more accurate in a 499 that any other brand of BB.
If I am right about the consistency of the spin, then a tight-fitting ball probably spins more consistently when shot from a smoothbore than one that’s looser. I know that holds true for a patched ball in a rifle.
What have I just said?
I’ve said several things, and they boil down to just a few important points.
1. The tighter a ball fits a smoothbore, gun the more accurate it will be. But there is a limit to how tight it can be.
2. As distance increases, smoothbore accuracy falls away rapidly. At some distance from the muzzle the accuracy becomes very poor.
Smoothbore accuracy with a round ball has already been tested several different ways. We may not have reached the limits of what can be accomplished, but I think we are in that part of the normal curve where enormous investments will be required for small returns.
Or, I could be completely wrong. If someone could figure out a way to consistently spin a BB like they spin plastic airsoft balls with Hop Up, maybe there is more accuracy to be gained. Or, if the uniformly dimpled BB — think golf balls — could be made maybe there is a quantum improvement in accuracy lurking around the corner.