I recently had the chance to borrow a rifle out of ANAa first limited production run of an innovated new rifle design.
Multi-Pump Airgun Designs
A good number of airgun hunters in the USA got their start airgun hunting using multi-pump designs that ranged from the Crosman 2100 to the cream of the crop in American airguns, the Benjamin – Sheridan 397 and Streak models. These pneumatic powerplants generate decent power for hunting, and can be quite accurate. An advantage of the design worth note is that the guns are fully self contained, and additionally the power can be adjusted by adjusting the number of pumps to suit a specific shooting application. Pump 2-3 times when plinking in the basement range, then up to 8 or 9 pumps when in the field hunting. But the flip side is that the gun must be pumped several times to get up to maximum power, and as in most designs of multi-pump rifles all the air is dumped with each shot, it is necessary to fully pump the gun between shots. This makes a quick follow up impractical. While there have been a number of multi-pump air rifles manufactured in the USA and Japan, the most popular and my personal favorite is the Benjamin and Sheridan design. In stock form this gun can be pumped up to 12 times and generate velocities in .20 caliber up to 685 fps.There are also companies that will do a tune to this rifle, such as Mac-1 Airguns Steroid model, which allows the gun to be pumped higher and utilize the charge more effectively. These guns can get the .20 caliber moving at around 900 fps with fourteen pumps, generating around 20 fpe.
Nibecker Quigley Series
Al Nibecker is a retired mechanical engineer living in Hawaii that like so many of us grew up shooting a Benji. After reading an article in one of the now defunct Airgun magazines, he decided there was a better way to build a multi-pump pneumatic, and that he was the guy to do it. His vision was to build a system that would generate much higher velocities with a lower number of pumps. Over the last few years Al has built a few prototypes and there have been a couple good reviews of these earlier iterations; I think the best reviews were written on the early prototypes by the well known airgun writers Thomas Jue, Robert Hamilton , and Tom Gaylord. For the last few years the Quigley has been a discussion point on the periphery of the hardcore airgunning scene as ANA went through the steps of gearing up for a limited production run of an updated design. In the coming section I’ll discuss my shooting experience with the Quigley, and in the sidebar will provide a quick review of the power plant technology that forms the basis of this multi-pump hunting rifle. I Finally Get My Turn and recently had the opportunity to borrow the gun for small game season. I arrived home from work one day and there was a big box sitting on my desk waiting for me. I ripped it apart to find a hard-case containing a unique and beautiful rifle. First thing you note when picking up this rifle is that it is a very good looking gun, the metal work is solid; fit and finish are flawless. The cocking bolt is substantial, and the unique pumping mechanism extending from forestock almost to the muzzle gives this gun a very different look from anything else in my gun cabinet. The stock on the test gun I was sent is really beautiful, nicely figured hardwood incorporating a well formed cheekpeice that provides a good sight alignment with the scope in low profile mounts. The forestock has grooves cut into it which does not fully mesh with my sense of aesthetics, but does provide a secure handle for pumping which is after all, the key requirement. This multi-pump gun has been described, discussed, and debated on the forums, and as mentioned previously the key aspects that make the gun special is comprised of the airspring and differential piston. I am not an airgun designer, a machinist, or a mechanical engineer. I am a practical shooter and hunter and what is relevant to me is that the product of this technology is a hunting rifle which does not have to be completely recharged after each shot, and allows the gun to be charged back up to 30 fpe with around 10 low impact pumps. Another unique aspect is that if a follow up shot is required in a hurry, the gun can be cycled one time to access the loading port, and then shot again quickly. The figure below shows the drop in velocity between four subsequent shots, and there is only a 10 fps drop between the first and second shot. I don’t believe there is another multi-pump airgun around that can replicate this capability. The pumping, loading, and shooting process is a bit more complicated than other airguns, but it doesn’t take that long to become acclimated. To start the process the bolt is pulled out and then down. When in the fully rearward positioned, the gun is cocked and the pumping handle is freed to cycle. Since the gun is now cocked, the safety should be deployed. The gun is pumped in a similar motion as conventional multi-pump guns, though it is not necessary to bring the handle all the way back to the starting position. This takes some getting used to, but by the time I’d pumped the gun a few hundred times for this evaluation, I had the hang of it! The loading port protrudes from the inside surface of the pumping handle, and on the last pump the pellet is seated backend first. This is an ergonomic loading process that was fast, easy, and required minimal movement (a good characteristic in a hunting gun). My only negative comment, some longer pellets like the Eu Jin did not fit and could not be loaded. This is only a minor inconvenience, and the pellets that did fit worked without a failure. Hunting and shooting the Quigley was pleasurable, I found that it balanced well and fit my frame as if built for me. During the three months I had this gun; it went along with me on several small game hunts for quarry ranging from squirrels to groundhogs. I ended up using Kodiak pellets as these heavy round nose pellets yielded good accuracy and terminal performance. The Quigley is a big rifle and I kind of felt as though I had a Kentucky long rifle in hand while stalking the woods. As mentioned the gun pointed well from just about any position I found myself shooting from; offhand, rested on a rock wall, or up against a tree trunk. When hunting squirrels I typically went in full camo and located a good location to sit and wait. The gun performed as well as any I’ve hunted with, allowing me to drop a pellet in the kill zone with precision, and several bushytails were dropped dead in their tracks by a heavy pellet moving at 800 to 900 fps. The largest animal that I shot with the Quigley was a groundhog that was hit squarely in the head at about sixty yards, dropping him cleanly. Squirrel hunting is where I experienced both the up and downside of the design; the upside is when I shot a squirrel and dropped him then quickly reloaded (which requires a single pump) and put a second in the bag. The downside was when I needed to recharge, there just isn’t a way to do it quietly or quickly. This is not a criticism, rather than a statement of the trade-off for having a fully self contained gun. The mechanism could be modified to provide hunting appropriate energies with only a couple of pumps.
Sidebar: How it works
The Quigley utilizes a couple of design innovations; an air-spring and a differential piston. To charge the gun an onboard pump which is housed in the pump handle of the air rifle is cycled. This mechanism is covered by a beautiful walnut forearm stock. During the pumping action, air is delivered under pressure through the check valve assembly and into an air-spring chamber. When the air rifle is completely empty, it requires many strokes to both charge the air-spring and fill the firing chamber. This is a one-time requirement, but the gun is precharged before shipment by the manufacturer. Subsequent shots require between 6-10 pump strokes depending on the power setting. Quite honestly, unless hunting larger quarry such as ground hog or raccoon, I don’t think more than six pumps are necessary. This Quigley also utilizes a differential piston design which is comprised of dual air storage chambers. The air-spring chamber is where the precharged volume of air is contained, and this volume is not expended when the gun is discharged. The firing chamber utilizes the air charge obtained by pumping the gun between shots. One of the unique design features of this rifle is a differential piston that separates the two chambers. The piston diameter in the firing chamber is larger than that in the air- spring chamber. Air under pressure enters the firing chamber through a regulated valve housed in the differential piston. The air-spring pressure must exceed the pressure setting of this regulator before air is allowed to enter the firing chamber. Adjusting the regulator adjusts the air-spring’s pressure and as a result the power output for the air rifle. ANA has tested several settings to find the right balance of power output, number of pumps, and pumping effort required. And while the gun I was testing generated around 30 fpe with 10 to 12 pumps, it would be possible to configure the gun to deliver 14 fpe with a single pump. Air enters the firing chamber where the larger area at the differential piston causes a force that exceeds the force on the air-spring side of the differential piston. This causes the differential piston to move backward, compressing the air-spring until the forces equalize. Additional pump strokes move the differential piston backward until the piston contacts the shoulder of the smaller air-spring cylinder. There is a small window in the pumping mechanism that took me a while to understand, but I finally figured out that it allows the edge of the piston to be visualized. When the piston reaches this point, it demonstrates that the air rifle is fully charged. The piston can actually move a short distance past this point to where the o-ring seal passes over a relief hole, providing a safety release that prevents the gun from being over-charged. The trigger is a conventional assembly, and when the sear is released the air-spring forces the differential piston forward. A constant force is exerted on the pellet substantially increasing the energy generated, above and beyond the simple expansion of compressed air. Again it should be noted that only the air in the firing chamber is utilized. If the gun is fired repeatedly without recharging, the air-springs charge will eventually be depleted. And once empty, the gun must be recharged before it can be shot again. It is fully charged from an empty state by pumping 60 – 70 times, initially filling the air-spring and once an adequate pressure has been achieved continued pumping will fill the firing chamber. The combined result of the air spring and the differential piston is a very efficient power plant that provides maximum power to the airgun hunter with minimal effort. As is often the case with innovation, it seems to be straight forward conceptually, once somebody with the vision and technical skills lays it out right in front of you, then walks you through the concept! I have borrowed freely from the explanations of Al Nibecker in describing his design, and have couched it in terms that I understand. I would urge interested parties with a more technical bent to contact ANA directly for additional information.