Postscripts Part 3
Air err and the Cowboy Lever Action
By Dennis Adler
“What we have here is a failure to communicate.” I’ve lifted this famous line from Cool hand Luke with the emphasis on cool because the air chamber in the new Umarex Legends Cowboy Lever Action is very cool, and in fact it needs to be re-explained and better understood. Traditional CO2 pistols and rifles use a single 12 gr. CO2 cartridge that fits in nozzle up (or horizontal on designs like the Diana Chaser and Cowboy Lever Action), but it is usually one CO2 to power the gun. When the seating screw is turned down, the CO2 nozzle pushes into the valve with its piercing pin and O-ring and the seal is complete.
As we know sometimes this fails, an O-ring wears out, was improperly installed, the piercing pin is not good, too short, breaks, all manner of things can go wrong, but rarely do. And most can be fixed.
To better understand how the Cowboy Lever Action works you need to look at the Umarex MP40 magazine which also uses two 12 gr. CO2 cartridges loaded back-to-back, just like the Cowboy Lever Action. The internal design of the MP40 magazine and the CO2 system in the Lever Action are essentially the same. You are loading the two CO2 cartridges with one nozzle facing into the CO2 chamber and the other facing up. When you tighten down the seating screw, the tube covers the nozzle of the CO2 cartridge and when tightened, forces both CO2 cartridges together pushing the first into the piercing pin at the front of the chamber while the piercing pin in the screw punctures the second. This releases all the CO2 from both cartridges into the CO2 chamber, which functions not unlike the air chamber in a precharged pneumatic pistol or rifle. A failure of one of the CO2 cartridges to be punctured only means that half the total volume of air is filling the chamber. The gun is still going to fire a peak performance because the air going into the valve system is a constant until there is too little air to allow a full charge. Thus you will get fewer total shots with only one CO2 pierced. The question is, “Why isn’t the second CO2 cartridge being pierced?”
I have discussed this today (Monday) with the Umarex technical department and there are several possible answers. First is that all CO2 cartridges are not exactly the same length. In a CO2 pistol this is rarely a problem because the seating screw has an ample margin for length when being tightened. In the Cowboy Lever Action it is a very precise fit and when you turn down the seating screw it only goes so far and you cannot tighten it any further. The two CO2 cartridges should be pierced by that point and the chamber filled with the CO2 from both. Now, if there is a variance in the length of the CO2 cartridges one might not be long enough for the two 12 gr. cylinders pushed back-to-back to be fully pierced by the top piercing pin. That is one possibility, and let me say this right now; Umarex does not recommend placing any object inside the chamber between the two cylinders to act as a spacer and create a tighter fit. You would be placing a foreign object inside an actual pressurized air chamber, not just between two CO2 cylinders.
The second possible problem is one Umarex began investigating which is piercing pins that may be too short or not sharp enough to pierce both cylinders when the chamber cover is screwed down tight. This could be a random problem as it is not happening with every lever action model that has been sold and has not occurred at Umarex during product testing. I have already tested three rifles and only one exhibited the problem.
At this point, after an odd mix-up in deliveries, I have three Cowboy Lever Action rifles on hand, and I am going to load all three, fire them out and then inspect the CO2 cartridges for piercing. I am going to use Umarex CO2 cartridges which are made to Umarex standards and should not be part of the problem (but my failed CO2 piercing with the gun used in Saturday’s article was loaded with Umarex CO2).
While I have been writing this today, the Umarex tech staff has been running tests on six randomly picked off-the-shelf Cowboy Lever Action rifles and none had a failure to pierce both CO2 cartridges. And they have a fix for the problem that should work most of the time unless there is a defective piercing pin. What they suggest is to use a drop of RWS Chamber Lube, not only on the tip of the CO2 cartridges but directly on the green O-ring on the seating screw (as shown in the pictures). If the ring is dry it will stick and not allow the screw to turn down as far; this could be the cause of the random problem.
I am starting with the second off-the-shelf Lever Action I received. I will load it with Umarex CO2, and use RWS chamber lube on the green O-ring before tightening it down. Going on the assumption that both CO2 cartridges have been pierced, and since I have to shoot it out, I thought I might as well chronograph again with a new rifle and the silver pellet-loading shells with H&N Sport Match Green 5.25 gr. alloy wadcutters.
I set up 25 feet from the target for the chronograph test. Average velocity was very consistent to previous tests at 661 fps with H&N and the majority of shots at 660 fps to 663 fps for the first 20 plus rounds. At the distance of 25 feet my best 10 shots were in two 5-shot groups measuring 0.43 inches in the bullseye and a second group, aiming below the bullseye, measuring 0.50 inches. Now, after that I kept shooting to count shots until empty. I stopped after 40 consecutive shots and chronographed the next 10, which averaged 628 fps. From there I shot until I could tell there was a drop in sound and power of impact on the target, at which point the total number of shots was 70. I ran one last chronograph test and shots were clocking 453 fps average. I got another 21 rounds out of the CO2 until empty, which is much further than one would normally go for any kind of accuracy, but I wanted to know what two pierced CO2 cartridges could deliver and that number appears to be 91. I unloaded the CO2 and both cartridges were cleanly pierced.
The second test with another off-the-shelf gun gave a total of 89 shots until empty and again both CO2 cartridges had been pierced. To prove the Umarex theory of using the RWS chamber lube on the green O-ring, I ran the final test using the first rifle that had failed to pierce both CO2 cartridges.
Again I used the RWS chamber lube before tightening down the piercing screw. I can recall that in my previous tests with this first gun there was a point at which the piercing screw would not turn any further and I believed it was down as far as it could go. Since loading the other two rifles I found that there was a little more turn down in the screw than I had experience before, but I attributed this to it being a different gun, but this is not the case. I was able to turn the screw down another two turns with the chamber lube on the green O-ring. With this same gun from my previous Postscript test I was able to get a total of 97 shots. I chronographed shots 71, 72, and 73 at an average velocity of 528 fps. The gun failed to fire on shot 98. Opening the CO2 chamber I found both CO2 cartridges were fully pierced.
So, the trick if you find yourself running out of air too soon and discover you have only pierced one of the two CO2 cartridges, is to not only put a drop of chamber lube on the tip of each CO2 as usual, but a drop on the green O-ring and make sure it is oiled all around its circumference before tightening it down.
The Legends Cowboy Lever Action might not have qualified as a candidate for Replica Air Pistol of the Year in 2018, but it certainly gets my vote for CO2 air rifle! Now if they can make a Mare’s Laig it can win Pistol of the Year some day!
We now return you to our regularly scheduled programming….