by Tom Gaylord ©2009
This article originally appeared in Airgun Illustrated magazine, but I thought it was interesting enough to bring it to you here.
Show an airgun of almost any type to someone who doesn’t know airguns, and they’ll call it a BB gun. Many will call it a Red Ryder. Veteran airgunners are used to this reaction from the public, but when they get with other enthusiasts the conversation becomes deeper and more precise. But not always! I discovered a few years ago that very few real airgunners are aware of just how a BB gun powerplant really works, so I thought I’d take the time to illustrate it.
Daisy helped me with this project by sending the shot tube and spring mechanism for one of their modern lever-action airguns. We’ll call it a Red Ryder, and it may well be, but the mechanism is common to more than just a single model. Because I have a modern mechanism to examine, I will report on just that; but if you take the time to look at the older models, you’ll see a lot of their design has been carried forward.
The BB gun powerplant is a hybrid of both the spring-piston and the catapult designs. The one we will examine uses gravity to feed the BBs, though other types, such as a spring-powered forced-feed magazine found in a Daisy model No. 25 pump BB gun, will work just as well with this powerplant. For the rest of this discussion, please refer to the illustrations as you read.
1. Prepare to fire
The gun is cocked and ready to fire, with the hollow air tube retracted just behind the next BB. The BB is held in place by a small magnet. So, even if you shoot straight down, a BB should come out. The “magazine” is nothing more than the hollow cavity formed between the inner shot tube (the true barrel) and the outer sheetmetal “barrel” of the gun. When the muzzle is elevated to cock the lever, gravity pulls the BBs down against a sloped surface that has a funnel-like channel at its lowest end. The BBs organize into a single column in this channel, and they drop down toward the BB seat where the magnet is located. All of this action depends on the muzzle being elevated, and nothing but gravity holds those BBs in place; so, they realign this way every time the gun is cocked.
2. Gun is fired
The sear has released the piston so the mainspring drives it forward. At the same time, the air tube that projects from the center of the piston has pushed the BB off its magnetic seat and started it down the barrel. A low initial velocity is imparted by this mechanical catapulting action. This is the catapult part of the powerplant.
3. The compressed-air blast
The piston has slammed to a stop against the back of the shot tube, squeezing all the air from the compression chamber and through the hole at the back of the air tube. The air is now highly compressed and travels up the air tube, where it exits behind the BB that is already in motion. It imparts a boost of velocity to the BB, accelerating it to its terminal velocity. This is the spring-piston part of the powerplant.
4. Gun is cocked
Cocking withdraws the piston and air tube assembly, making room for a BB to roll down and be captured by the magnetic seat. The gun is now ready to fire again.
That’s the cycle of the BB gun powerplant. As you now can see, it relies on both a catapult action and a spring piston to do its job. The combination of these two forces works like the booster rockets in a space vehicle; only in this instance, the boost means that the mainspring can be made light enough for younger folks to cock, yet still supply adequate power to launch a BB.
Spring & piston assembly: The mainspring is held captive by the piston assembly. A spring anchor in the gun holds the back of the spring steady when the cocking lever withdraws the piston and compresses the spring. Notice the long air tube that projects from the front of the black piston seal on the right. It fits inside the shot tube assembly, where it aligns with the barrel.
There are other types of BB gun powerplants, of course. Some are common, like the CO2 guns that simply blast the BB out the barrel, but others are very subtle. In future issues we may look into some of these powerplants as well, but the one we looked at here is by far the most common and most important type of BB gun powerplant there is.