What is a bolt-action?
by Tom Gaylord, a.k.a. B.B. Pelletier
Today I’m writing about something that seems to confuse many people. It’s tied to how an airgun works, and I want to discuss it in detail for you. But first, let me tell you what motivated me to write today’s report.
The following is a real question I have heard many times.
I’m looking to buy a gun and it says the gun is a repeater. Please explain to me what a repeater is. Do I have to cock it for every shot? I don’t want it if I have to cock it for every shot. I want to just be able to pull the trigger and the gun fires.
I wrote the report that’s linked above for those new shooters who have trouble understanding the definition of a repeater. Some shooters don’t understand the difference between a semiautomatic action, where the trigger is pulled to fire the gun every time, and a repeater that must be both cocked and also load the pellet before it’s ready to shoot.
Last week, I discovered that this confusion goes even farther. A customer wrote in to Pyramyd Air that one of the FWB target guns was not a bolt-action like they had listed…but it was a sidelever. The gun has a lever on the left side that operates the bolt. When the lever is operated, the bolt slides back and forth in the pellet trough and pushes the pellet into the breech to the same depth every time. It’s likely that other airgunners may understand it the same way, which is why I wanted to address it in the blog.
Yes, that lever on this Feinwerkbau rifle does cock the gun; and yes, it is on the side…but that doesn’t make the gun’s action a sidelever. That lever is called a flipper by shooters who borrowed the term from biathlon shooters, whose cocking levers are flippers that work back and forth.
A sidelever refers to a cocking mechanism for a spring-piston airgun. The lever connects to the piston, pushing it back to cock the mainspring. The FWB 700 is a PCP, not a springer. The fact that it has a lever on the side is coincidental. That lever, which is properly called a flipper by the shooters who use it — is just a linkage to the bolt. Edith told me she often gets comments that are like this one, so I thought I would address this today.
A bolt-action gun has a cylindrical metal rod called a bolt, whose job is either to push the pellet into the breech or sometimes to also act as a conduit for the compressed gas that fires the pellet into the barrel. How the bolt is designed and how it works affects the accuracy of the airgun.
The bolt nose of the Benjamin 130 bolt is hollow — like many CO2 bolts. But this one is shaped to hold one steel BB during loading.
Only airguns today
When I talk about a bolt-action gun in this report I will be referring only to airguns. This is one area where firearms and airguns differ quite a lot.
What do bolts do?
Airgun bolts do a couple of things, and they do them to different levels of perfection. So, it’s important to know exactly what a particular bolt does if you want to know how to make a gun work its best.
The first thing an airgun bolt does is seal the compressed gas inside the barrel. Some bolts have hollow noses to conduct the compressed gas into the barrel, where it gets behind the pellet. But not all of them do. But they all seal the barrel, so the compressed gas works on just the pellet.
The Crosman 180 CO2 carbine has a synthetic seal that the bolt presses against the rear of the barrel to seal the gasses. This bolt is only for loading the gun. A separate cocking knob pulls the hammer back.
The second thing bolts do is push the pellets into the back of the barrel. But here’s a big distinction since the back of the barrel sometimes isn’t actually where the rifling begins. The back of the barrel may be drilled out larger than the rifling and just be a chamber where the pellet sits before firing. If the pellet does not touch rifling in this section, accuracy may suffer.
If the bolt doesn’t push the pellet into the barrel to the point that the rifling engraves it — at least on the head, if not both the head and skirt — then it’s possible that the pellet will be slammed forward on an angle and enter the rifling out-of-line with the axis of the bore when the gun fires. The angle may be slight, but it sets up an imbalance that’s acted upon by the airstream when the pellet leaves the muzzle. The drag is not aligned with the axis of the pellet and can start a small wobble as the pellet goes downrange.
Some bolts have a long thin nose section that we call a probe. The probe pushes the pellet deep into the breech; because it’s thin, it also allows the maximum air to flow around it. While this sounds like such a good idea that we would want all bolts to have a probe, you have to remember that the inside of every pellet skirt is different. The probe sticks deep inside some pellets and doesn’t push them as far into the rifling. But it hits the flat wall inside other pellets and pushes them very deep.
Repeating airguns use the bolt to push the pellet through the clip or magazine and into the breech. This is one more relationship that must be considered.
Matching the shape of the bolt nose to the pellets you use is important for accuracy. And sometimes an airgunsmith will change the shape of the bolt nose to get increased performance from a certain gun. This is very common with the vintage CO2 single-shot air pistols such as the Crosman Mark I and II and the S&W 78G and 79G.
The bolt nose on this vintage Crosman Mark I target pistol is stock — just as it came from the factory. You can call this nose a probe because that’s how it works. But look at the next picture to see the contrast. Like the Crosman 180, this bolt only loads the pellet. A separate set of sliding tabs cock the hammer.
The bolt probe on this S&W 78G pistol looked like the Crosman, above, when it was new. An airgunsmith has thinned and even shaped this probe to allow gas to flow around it more easily. Just this modification by itself added velocity to the gun. This is another bolt that only loads the pellet. Cocking is done separately.
Like the custom tuners, Crosman made their Marauder bolt probe thin and long. It pushes the pellet from the magazine into the breech and also seats the pellet deep in the rifling. Because it’s thin, air flows easier around and past it, giving better efficiency.
Of course, not every bolt has a probe. Many get along very well with just a simple bolt nose that may even be flat because it fits the shape of the back of the pellets it’s designed to shoot. The Crosman-2240 air-pistol is one example of this.
Finally, some airguns are made to fire both steel BBs and lead pellets. People wonder how these guns are able to be rifled and still shoot steel BBs, but the factories have figured out how to do it. And, yes, the steel BB does wear the bore faster than the lead pellet. In fact, the lead pellet probably doesn’t wear a rifled steel bore at all, at least in terms we can comprehend. There are target rifles owned by clubs that have millions of shots on them and, while they look pretty doggy, their bores are like new.
A gun that shoots steel BBs probably has a flat magnet in the tip of its bolt, so there’s no possibility for a probe. On the other hand, if the tip is wide enough, it probably still shoves the pellet into the breech because the bolt will slide only a short way into the pellet’s skirt. Again, the shape of the inside of the pellet skirt will affect how this works.
The bottom line is that the shape of the bolt really matters a lot for airguns. It has several jobs to do, and its shape determines how well it will do each one. The next time you look at an airgun that has a bolt, give some thought to how well the bolt tip matches the pellets you want to use.