Some thoughts on airgun projectile stability
by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- Pioneer airbow
- Projectile finish
I’m writing this from my hospital bed on Saturday, though I hope to be discharged later today. I would like to thank Val Gamerman for covering the blog for me last week. I was unable to do much of anything, and my thanks to all of you for keeping things going. This will be short, because of my situation. Let’s talk about airgun projectile stability today.
When I shot the Benjamin Pioneer airbow at the SHOT Show this year I was amazed by the accuracy it gave. Not just when I shot it, but also there were two cases where one arrow went inside another one at 30 yards. Television’s Mythbusters proved that a regular longbow cannot do that because the arrow is constantly flexing as it flies, but the Pioneer pushes the arrow from the tip (it’s hollow inside) rather than from the back end and it doesn’t flex in flight. That got me thinking about what has been done about airgun projectile stability and what remains to be done.
Most people know that rifling spins the pellet and stabilizes it while it flies. But there is a lot that hasn’t been done in this arena. Most airguns are rifled with a 1:16″ twist rate that seems to work pretty well. There have been some barrels with a different twist rate, but more research needs to be done. I did a huge test on barrels with 3 different twist rates that you may want to review. I was not able to match the pellet to the twist rate in my test, but that’s a place when more could be done.
The Smooth Twist barrel from FX and also from the earlier Swedish Excellent is another place to be considered. Has the optimum combination of rifling length, twist rate and rifling depth been found? And has it been paired with an optimum projectile yet?
Another place to consider is the gain twist rifling. I don’t believe anything has been done with that in an airgun. Would a gain twist that starts at no twist and increazses to 1:16: be better that a straight barrel? Would it act more like a Smooth Twist barrel?
We saw a pretty dramatic example of what Hop-Up can do for an airsoft BB last week. Hop-Up puts a backspin on the ball before it leaves the barrel. Would it even be possible to put a Hop-Up on a gun that shoots steel BBs? A number of readers have asked this and a couple are experimenting with it.
One area that has been left alone is the surface finish of a pellet or BB. We know that golf balls fly better because of the dimples on their surface. Would that also held BBs in flight? Would the BBs have to be spinning for it to help? What would the indents (or protrusions) have to look like? How deep/high would they need to be?
Would changing the surface finish of a diabolo pellet have any affect on stability? Where would the finish go?
These are a few of my thoughts on the stability of projectiles in flight. Other thoughts might include darts, conicals bullets in big bore airguns and more. What have I forgotten?