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Sometimes, in the pursuit of perfection, we leave alot of fun in the dust. Air guns are complex instruments, even in their simplest forms. It's a bit odd how things are viewed. Air guns are often seen as simple stepping stones from which we eventually grow into firearms. In fact, nothing could be less true. The firearm has one big trump card - an exploding powder charge. Firearms themselves, are simple. The charge is touched off and the shot is away.
The first simple firearms were no more than a chamber with a big hole in one end and a little hole in the other. The powder and projectile went in the big end, a fire was applied to the other end, and - bang!
The first pneumatic arms were a bit of a different story. First, a pneumatic rifle must have a pressure vessel to store compressed air. Such a vessel usually has an intake and an exhaust valve. Two valves which must open, reset, and remain consistently air tight. High expectations, and this is before you start to built the gun at all!
During firing, the blast of air from the valve must be routed (inside pressurized passages) to the projectile before it can push it. No simple task. This is the reason that historically, air guns were always prized as complex instruments - almost mystical in quality. There's no such thing as a "Simple" air gun.
That said, it must be realized that the bolt action, single shot rifle is a very complex project to build from scratch. It's not just a jumping off point. Sometimes, there is the pressure to add on and add on until the project has grown away from your true need. It's also easy to order up something that has half enough features for one task and half enough for another and not a complete set for either. I would suggest that you consider the fundamental usage for the gun you wish to buy, and make certain that you tailor a complete set of features to that purpose.
THE PRESSURE IS KILLING ME . . . .
Let's talk about the pressure of custom air guns - no, not making them, designing them. Still lost? I'm talking about how much pressure to design the valves to run off of. Here in the U.S.A., people like to run things wide open. If it has ten settings, why use one through nine? Let's have it altered to include "eleven".
But, take that 3,000 psi tank and fill your gun a couple of times and what do you have? A whimpy gun cause you now only have 2,700 psi in the tank. Fill it a couple of more times and half your power curve is gone. You have something that wants a 3,000 psi diet and can only get 2,400 now. Do you understand? It's not that you need 3,000 psi to do the work, but the designer designed a valve that requires 3,000 psi to achieve the given task. It's starved on less pressure due to design.
Let's understand reality here. What are we trying to actually do? Project a pellet of a certain weight at a certain velocity a certain number of times. That done, what does it matter what pressure does the task? Fact is, if you know what you are doing, you can design the complete system to run at far lower pressure. Most of my Ranger series guns are designed to run around 2,000 psi. What's the matter with me? Nothing. I can fill my guns over and over and over and perform the same tasks while others are setting their tanks aside to go back to the scuba shop.
Let me put it another way that will be familiar to you: Say you want an automobile to travel 400 miles between fill-ups. You want to travel at an average speed of 70 mph. Those are the requirements. Now, I say I can give you such a car and it consumes 28 miles per gallon doing so. Now, why would you want me to offer you a car that only does the same tasks but at a consumption rate of 14 miles per gallon. I said, the same tasks exactly but for twice the consumption rate. Silly. Same with the guns. Use what you need to do the task. I've done alot of research and development work to offer guns which are "fuel efficient". You give up nothing but many more trips to the scuba shop.
Now, when it comes to large bore guns, less is definitely more. I have a new gun coming out that gives over one hundred foot lbs. of muzzle energy with only 500 psi. Interested?