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Sorting out Caliber Vs. Power

(Tossing in Shots per fill as well)


Some of you have asked regarding caliber's effect IF the foot pounds of energy were equal between ... say 32 and 45 caliber PCPs.

You'll get all sorts of opinions. Since you've asked me (and this is my site) I'll tell you my experience.

Let's lay out some numbers:

Example 1. Take a 32 caliber slug of 115 grains @ 850 fps and it equals 184 fpe.

Example 2. Take a 45 caliber slug of 215 grains @ 621 fps and it equals 184 fpe.

Now, 99% of the people will jump on the 850 fps bandwagon (because it's closer to the magic 1,000 fps that all airguns are supposed to dream about). Yep, the trajectory is flatter. No, it won't deliver as much on-target energy. What accelerates faster will also slow down faster. And, a lighter projectile will not retain as much of it's muzzle energy at distance.

In addition, that big surface area of the 45 slug will offer more of a resistance (read energy transfer) than the small diameter slug.

So very much of airgunning depends upon your background. If you come from a background of firearms, Heaven help you. You'll have spent decades laughing at the guy at the range who was STILL ONLY shooting 2,700 fps. For you, turning the dial down to 1,000 fps will be a humbling fall from grace. Now, if you are fortunate enough to have come from a background of archery (where all the magazines refer to 325 fps as "Blazing fast", then winding velocity up by three times will be quite a hoot.

Actually, neither one matters a whit. It's irrelevant. Airguns are not firearms, nor are they bows and arrows. They are airguns. They function as airguns function. They are limited by the physics of expanding air. So, depress yourselves or become giddy, no matter ... airguns function as the rules of physics allow. Some few will become intrigued by learning how airguns function and develop the skills required to adequately use airguns. Others will forever be depressed and hope against hope that the next time they ask regarding velocity, the numbers will be higher. "Maybe next year's model" will be able to cheat physics ... but ... I doubt it.

What I attempt, as an airgunsmith, is this: To use the rules of physics to project the most energy (with air) to the greatest distance, and with the greatest degree of accuracy. That's the ultimate from my point of view. Now, there are many other schools of thought which raise individual parts of the equation above the rest. The "velocity rules" school finds they must cut way back on the weight of the projectile to off-balance the equation so the velocity portion wins. The "energy rules" school finds they must fire a very large projectile from a very large caliber and consume huge amounts of air doing so. You'll hear of guys jamming huge slugs in some of the Philippine brass rifles or popping out big caliber ball from converted production pistols. The velocity numbers are often in the 300 fps range in order to make the power numbers rise.

I make shoulder fired rifles. Compromises must be made along the way. There is so much you can do with the energy which may be stored aboard a reasonably sized rifle. And, this brings us to "shots per charge" .... again. A choice is made. More shots at a lower energy level, for a given storage of air. OR ... less shots at a greater energy level, for the same given volume of air. No magic involved. Efficiency of design will help ... yes ... but not to the degrees most people think.

Folks who are interested in big bore airguns will know of the few commercial offerings in the field. I have a customer waiting for one of my rifles. He also owns two of the Korean rifles ... a 9mm single shot and a 45 single shot. The other day he sent me some velocity numbers and shots per charge data. I appreciate hearing from all of my customers who share their shooting stories. He won't mind me sharing some data here. He's not under any impression that his rifles are delivering state of the art power, though they are well worth the money and quite enjoyable. Let's look at a summary of the information he shared:

Both of the rifles filled to 3,000 psi. Both delivered about 18 shots. WOW! The more the better I always hear. And, can you imagine that for some of my own rifles, I only quote 3 shots onboard? I must be a really lousy Airgunsmith! ..... (I heard that .... ;?)

So what's the scoop? Well, these rifles were firing their projectiles in the 500-600ish fps bracket. Over the 18 shots, the velocity varied maybe 130 fps. The 9mm was putting out 74-118 fpe and the 45 was making 100-147 fpe. Now, my customer wasn't bragging about the number of shots, however; I've heard it from many other people for years. Those folks who are bragging, don't seem to understand (or are conveniently forgetting to mention) the very low velocity numbers; and thus the low power band of their rifles. When I make available state of the art performance (at power levels of 235+ fpe in 32 caliber, 500+ fpe in 45 caliber, and 650+ fpe in 57 caliber) I must burn fuel to give it. Thus, my 45 caliber that actually offers 1,000 fps velocity, does NOT get 18 shots per fill. And, the rifle that offers a string of shots within very close velocity tolerances, is doing something quite difficult. Lastly, the rifle that offers you relatively high energy at a much lower than commercial psi fill pressure is doing something quite unique as well.

Maybe this little word picture will put the final frame around the phenomena. Let's watch two kids arguing about who has the most money: One has five quarters in his pocket. The other has twenty pennies in his pocket. It's often the kid with the pennies who loudly proclaims he has more money. And, he does indeed have more "money" ... just of a much lower potency.

So, I make many different rifles. It depends upon the need of the client. I can cover you up with shots per charge if you'll take less and less energy per shot. I can give you that big ole bulging pocket full of pennies. Or, I can give you a handful of quarters. Your choice. While that's rare enough ... you also have the choice of some of my work which will even give you a couple of half dollars!!! ;?) Those are magnum powered versions of each caliber, which are designed to give you the best possible compromise of velocity and power projection for their individual calibers.

OK ... coffee's gone. Back to the shop.

Questions ...

 e-mail Gary direct