Best engineering practices for airguns
by B.B. Pelletier
While installing a scope the other day, I encountered the same problem that’s bothered me for years with scope mounts. How come the manufacturers make them to use three different-sized Allen screws when it would be just as easy to design them to use only one size screw all around? That way, only a single Allen wrench would be required to install the mounts and to mount the scope. That got me thinking about airgun design in general. Why is it that most manufacturers haven’t got a clue as to how their customers will use their guns? Most of us simply speculate that that is the case, but I’ve talked to enough manufacturers and engineers to know that it’s true.
What is needed, I think, is a handbook of best engineering practices that can be followed when designing airguns so foolish mistakes are never made. It would be a tutorial for the newer designers and a place to record the institutional memory for those with experience in the field.
Since there’s no way such a manual will ever be compiled by a manufacturer, I thought it would be useful if the readers of this blog could pool their experience and create one. We would share it with anyone interested in it. Who knows? It could ultimately help someone design an airgun the way we think they should. Even if nobody ever reads it beyond us, it’ll be a fun thing to do.
So, today I’m going to propose a few design practices that I think would be helpful to airgun designers. You’ll quickly see that these “practices” are not specific instructions. They’re more like the corporate values of our hypothetical design team. You can comment on them and submit some practices of your own. I’ll copy the practices you submit and paste them into a document for the record. With the level of expertise available in our readership pool, we might come up with an interesting read.
I can’t think of a good way to categorize these practices yet, so I’ll just write them down as they come to me. When there’s a larger body of them, perhaps some order may be suggested.
1. Use fasteners of common size whenever feasible.
Common-size fasteners reduce the number of tools needed to work on a gun, plus they simplify the supply chain. Common size refers to the size of the tool needed to tighten the fastener, as well as the thread pitch and count and the diameter of the shank. Obviously, the length of the fastener shank depends on the application; but, whenever possible; that should be kept standard, too.
2. Select materials that are understressed for the application.
Do not select a material that only meets the performance requirement, but one that exceeds it. For example, do not use a seal that seals only when it’s fresh and new, but one that still seals a long time after it’s put into operation. As an example, a seal with a lower durometer rating may work well when new, but over time it may deform due to its softness, while a seal with a higher rating will continue to hold its shape and work much longer. Or, a synthetic part may be barely adequate for the application, while a metal receiver would continue to function for a much longer time. If you know beforehand that you’ll be building the receiver out of metal, you can design it to require less fabrication.
For this practice to work in the real world, we need to be practical. If a synthetic receiver, for example, costs $3 to manufacture or purchase, while a steel receiver would cost $14 with an added cost of $7 of overhead expense (when you make it rather than buy it you have to pay the workforce and amortize the tooling into the cost). It makes sense to go with the synthetic receiver because any cost in manufacturing has to be multiplied at least five times to allow room for wholesale tiers and profit. When the cost is very close, I’m suggesting to go with longevity over cost, alone.
Okay, now I’m going to get up on my soapbox. If I owned a manufacturing company and someone who worked for me uttered the phrase “build to a price” I would be extremely angry. As far as I’m concerned, anything that’s “built to a price” is made by bottom-feeders who manufacture products for landfills. As long as I’m in business to make things, I want them to be the best that I can make them. However, I’m not foolish about this. I would build rifles like the Bronco, for example, instead of something even cheaper that shoots twice as fast for the limited time that it works. The Bronco is a nice air rifle, but it doesn’t have a Rekord trigger or a Lothar Walther barrel, so it’s still very affordable. It’s a good package of performance that should last for centuries rather than months. I recognize that the Bronco won’t thrill the armchair enthusiasts with useless high velocity, but neither will it turn off thousands of potential newcomers to airgunning with crude performance that quickly sours their opinion of the whole hobby. There — I’ve said my piece and am now stepping down from my soapbox.
3. When designing guns to use common platforms, invest more time designing those platforms to adapt to as many applications as possible.
Time spent in up-front engineering pays huge dividends downstream when no additional work needs to be done to make significant changes. In other words, if you’re designing a single-shot action, do so with an eye toward adding a repeating function later on.
4. Have your design team and marketing team test the gun before it gets produced.
How many times have I shot an airgun, only to remark to myself: “I bet nobody in the company ever tested this.” If they had, they’d have recognized how bad it is. It doesn’t take an engineering degree to recognize that an air rifle is too difficult to cock (e.g., Hatsan 135), falls apart within a short time or has way too much barrel droop to use a scope (e.g., any Diana 34), etc.
5. Don’t offer features that shooters don’t need.
This is the age-old marketing ploy: “If we can’t advance the technology, give them something different.” It doesn’t matter that they don’t need it — offer it anyway so the list of features on the outside of the package is longer. I’m referring to things like scope sights that you can see through to supposedly enable you to use the open sights while the scope is mounted. No experienced shooter does that, but you’ll find a mountain of see-through scope rings on the market. The truth is that those see-through rings are nothing of the kind. The 15-foot-long aluminum extrusion they were cut from was made with that hole to conserve aluminum, period. Yet, they’ll tell you it’s both to lighten the rings and to see through.
6. When you can, design in a modular way.
Make a trigger whose parts are all contained in one unit that can be handled outside the gun without regard to losing parts. Make a powerplant that can be disassembled in a straightforward way with no need for holding fixtures or jigs.
Well, there you have 6 of my ideas for the better engineering of airguns. Now, I’d like you to add yours in the comments section. Don’t strain to invent something new, just to have a submission. Your ideas should be things you’ve wanted to say for a long time but were unable to find the right place to say them. I’ll save those that are clear and understandable; and, if there are enough of them, I’ll publish a list of all of them in the future.