by Tom Gaylord, a.k.a. B.B. Pelletier

Neat fix for bulk-fill CO2 guns
Part 1

Crosman 116 pistol
Crosman’s 116 bulk-fill pistol is a .22-caliber single-shot pistol.

Today, we’ll look at the velocity of the Crosman 116 .22-caliber bulk-fill CO2 pistol. A couple things will complicate this test. First is the fact that the pistol has adjustable power. I’ll account for that with several power adjustments, but that isn’t all that’s going on.

The bulk-fill process is itself somewhat complex; because if the bulk tank doesn’t have enough liquid CO2 in it, or if the tank and the gun are both warm, the fill will be less dense and will therefore produce fewer total shots. Let’s look at the fill process before we examine the gun.

The bulk-fill process
Filling an airgun from a bulk tank requires that the filling tank has sufficient liquid CO2 inside to transfer the maximum amount possible to the gun. When I say the maximum amount possible, I mean what’s maximum under safe operating conditions. It’s possible to overfill a CO2 tank or gun and create a dangerous condition.

CO2 pressure is controlled by the ambient temperature rather than by compression. If you make the CO2 storage vessel volume smaller somehow, you don’t compress the gas inside. Instead what happens is more of the gas condenses into liquid. It will continue to do so right up to the point that there’s 100 percent liquid inside the tank.

While that sounds good, it isn’t; because when the liquid inside the tank heats up, it tries to expand into gas again. As long as there’s space inside the tank for the liquid to evaporate into gas, you’re safe; but when the safety volume is filled, all the liquid CO2 can do is increase in pressure. It does so at an astounding rate, quickly developing over 10,000 pounds per square inch at temperatures that are still well within human tolerance. That’s why tanks rated for CO2 storage contain safety burst disks to prevent the tank from becoming a dangerous bomb. It’s also why several airgunners have been startled when their tanks’ burst disks actually burst while stored in their cars on hot days. Once the burst disk ruptures, all gas is lost and the burst disk must be replaced before the tank can be used again.

These days, most airgunners get their bulk tanks filled at paintball stores; but in my day, they filled them at home. There were even larger bulk tanks of CO2, holding 20 pounds of liquid. They came from the food and beverage industry, or they were large fire extinguishers. I own 2 of these 20-lb. CO2 tanks that I use to fill my bulk CO2 tanks for guns.

Filling bulk tank
The 12-oz. paintball tank is coupled to the 20-lb. CO2 tank for filling. This big tank has a siphon tube, so only liquid escapes the valve when it’s in the upright position. Couplings are custom made for this.

Once the smaller bulk tank has been filled, it’s time to fill the gun. Remember, the object is to transfer as much liquid CO2 as possible for a dense fill. That doesn’t give more power — it gives more shots. The CO2 controls the pressure, depending on the ambient temperature.

filling gun
The 12-oz. paintball tank is then coupled to the CO2 gun like this. With the CO2 tank hanging down, the liquid in the tank is just behind the valve, where it will flow readily from the tank into the gun. This paintball tank has a special adapter with a wheel to control the opening of the valve.

Filling the gun takes just a few seconds. It actually makes a sound, and you can tell when it’s full because the noise of the transfer stops abruptly. The outside of the gun may become cold and wet with condensation when the new CO2 inside evaporates to gas. As long as you do this transfer at room temperature, everything will be safe, for the liquid CO2 will evaporate and stop the fill before the gun accepts too much liquid. The gun is now full and ready to test.

Shot count
Because the pistol has adjustable power, I tested it on high power first. I found that there were 21 good powerful shots with the gun set on the highest power. Then, I adjusted it to medium power and finally to the lowest power. Medium power was very close to high power in all respects, but on the lowest power the total number of shots per fill increased to 32.

Crosman Premier
This is a Crosman gun, so Crosman Premier pellets sounded like the best place to begin. On high power, they averaged 390 f.p.s. The range went from a low of 384 to a high of 409 f.p.s. At the average velocity, this pellet generates 4.83 foot-pounds at the muzzle.

On medium power, they weren’t much slower — averaging 386 f.p.s. But on low power, they averaged 331 f.p.s. for an average 3.48 foot-pounds of energy.

RWS Hobbys
Next, I tried RWS Hobby pellets. In .22 caliber, these weigh 11.9 grains and average 423 f.p.s. in the test pistol. That’s a muzzle energy of 4.73 foot-pounds. The low was 413 f.p.s., and the high was 435 f.p.s. On medium power, Hobbys went an average 402 f.p.s.; and on the lowest power, they averaged 369 f.p.s. That’s good for a muzzle energy of 3.60 foot-pounds. On low power, the low velocity was 355; and the high was 383 f.p.s.

RWS Superdomes
The last pellet I tried was the RWS Superdome. This pellet weighs 14.5-grains in .22 caliber and is a favorite among many airgunners for all 3 powerplants. On high power, Superdomes averaged 376 f.p.s. The low was 362, and the high was 391 f.p.s. At the average velocity, Superdomes generated 4.55 foot-pounds. On medium power, they averaged 367 f.p.s.; and on low power, they averaged 345 f.p.s. On low power, the low velocity was 341, and the high was 348 f.p.s. At the average velocity, they generated 3.83 foot-pounds of muzzle energy.

The trigger-pull on the test pistol measures 4 lbs., 2 oz. That’s a little heavy, but it’s very crisp, so it’s going to be okay for target work. There are no provisions for adjustment on this trigger; so if I want to change the pull, I have to do some gunsmithing.

Odd note
I noted that when the gun was fully charged, the velocity always started lower and climbed into the good range — just like a precharged gun that’s overfilled. On the lowest power, the gun sometimes failed to discharge. CO2 guns aren’t supposed to do that, so I assume either the valve return-spring has weakened over the past 60 years, or someone has been inside the valve and changed things. Either way, that’s a good reason for an overhaul. The transmission sealer worked and now so does the gun; but it doesn’t work exactly as it should. That’s also probably why the number of shots per fill was lower than expected.

Overall evaluation
To what can I compare this air pistol? How about to a Crosman 2240, which is also a .22-caliber single shot but runs on 12-gram CO2 cartridges, but in many other ways is like the test pistol? The 2240 has a 7.5-inch barrel, so it’s a little faster than this 116 with a 6-inch barrel (Premiers averaging 448 f.p.s. to the 116’s 390 f.p.s.). Its sights are fully adjustable. The grip, while a bit larger, feels very much the same. So, if a 116 and bulk-filling aren’t in your future, know that there’s a good alternative.

I do think the test pistol is shooting a little slow for a 116. Maybe it would be best to get it overhauled to see what one in top condition can do