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

Part 1
Part 2

Umarex Fusion rifle

Umarex Fusion CO2 rifle

Part 3 of most reports is the day we test accuracy. Sometimes, we test accuracy more than one time; but Part 3 is usually when we test it for the first time. But that isn’t going to happen today. Blog reader mikeiniowa told us that the Umarex Fusion CO2 rifle rifle has both adjustable power and an adjustable trigger. I said I would look at that in detail when we got to it. Well, today’s the day.

The CO2 cap assembly
Before I get to either of those things, however, I want to talk about the CO2 cap in detail. I promised I would show you how this works, so I’m going to take it apart and show you the internals. I’ll also try to describe why the cap is as complex as it is.

Umarex Fusion rifle CO2 cap assembly
The Fusion CO2 cap disassembled. The parts are described below.

Let’s examine the parts, starting at the right of the above image. That rounded cap is the cover for the gas exhaust screw. It has left-hand threads, so you must remember that because it’s made of plastic and can easily be stripped. Next to that is the threaded metal cap that holds the CO2 cap assembly to the rifle when there’s pressure in the gun. One of our readers noted that this threaded metal cap is separate from the main CO2 cap assembly. It has to be made that way because of the o-ring. When gas is in the gun, the o-ring swells and will not permit the CO2 cap to be removed. If the threaded cover was attached to the main cap assembly, it would be locked in place until the o-ring finally returned to normal size — you couldn’t even turn it. Back in the 1960s, it sometimes took days and even weeks to get the CO2 cap out of some guns because of the way they were designed! The threaded cap retaining ring, as I call it, was created to allow the cap to be removed when the main cap was frozen in place from internal pressure.

Crosman came up with the idea of making this threaded retaining ring separate from the main cap assembly. That allowed the threaded ring to be taken off the gun, and then the main cap assembly could be removed from the gun by wiggling it from side to side. That one change reduced the time to remove the CO2 cap from days to minutes! The Fusion uses the same design to achieve the same result. But if the o-ring didn’t swell in the presence of the gas, this type of design wouldn’t be necessary.

The pressure-relief screw seen above the first 2 parts on the cap pushes against the brass part seen to the left. That opens a way for the gas to escape. The coiled spring holds the brass valve seat shut at all other times. This is why it is important to back off the pressure-relief screw when piercing the CO2 cartridges.

The long part with the orange o-ring around it is the main cap body that all the other parts assemble to. As seen in the picture, it’s a hollow plastic tube. And the part to the extreme left houses the piercing pin. Though the part is plastic, the piercing pin is a metal insert.

Umarex Fusion rifle piercing pin
The piercing pin inside the plastic cap is a metal insert.

Trigger and power adjustment
Okay, now we understand the CO2 cap, let’s look at the adjustments on the gun. To get to them, the action has to be removed from the stock, and it isn’t as straightforward as it is on some guns. The forearm has one screw at the bottom front. Once it’s out, the trigger unit has come out. That’s where it gets complex. The rear screw fastens a separate piece of plastic at the back of the triggerguard and holds the rifle to the stock. Take it out, and the barreled action is loose in the stock; but 2 more trigger screws have to be removed.

Once the trigger unit was outside the gun, I saw what it is — a unitized trigger that is highly based on the Crosman 160s trigger. It isn’t a copy, but it works the same with most of the same parts. Only the safety slide is different.

Umarex Fusion rifle CO2 cap assemblyCrosman 160 CO2 rifle crossbow trigger nut
From Sir Ralph Payne-Gallwey’s book, “The Crossbow,” (published in 1903) this illustration of a 15th century crossbow nut shows how a great force can be overcome by a smaller one.

Crosman 160 CO2 rifle trigger graphicFrom the Beeman R1 Supermagnum Air Rifle book.

Umarex Fusion rifle trigger
I didn’t have to open the Fusion trigger to see that it’s very similar to the Crosman 160 trigger.

Umarex Fusion rifle trigger sear adjustment
Apologies for the blurry image. Like the Crosman 160 trigger, the sear engagement is adjusted by the small screw at the top. There’s no screw in the hole below that, which is the trigger overtravel adjustment. The large Allen screw at the bottom adjusts the trigger return-spring tension, which is the weight of the pull.

Umarex Fusion rifle trigger sear adjustment from top
The threaded sear adjustment screw is shown at the right (arrow).

I tried adjusting the trigger, but apparently I don’t know the secret, if there is one. I couldn’t take the second-stage creep out of the sear without making it impossible to cock the rifle. I settled for lightening the pull to 3 lbs., 5 oz. But the trigger still had a lot of second-stage creep.

I’m hoping mikeiniowa will tell me that I missed the trigger optimization screw that fixes everything; because each time I adjusted the trigger, I had to assemble the rifle in the stock to test it. I bet there’s more to this trigger than I’ve discovered. And, of course, none of this is in the manual!

The power adjustment is very straightforward. Simply tighten or loosen tension on the striker spring with a screw located at the rear of the receiver.

Umarex Fusion rifle power adjustment
The power adjustment screw and locking nut are located at the rear of the receiver.

Observations
The Fusion has some interesting designs, but I don’t think they were done by an airgunner. Each area shows a lot of attention to detail, but the complexity of the CO2 cap shows the designers were either unaware of the advances that have been made in CO2 gun technology, or for some reason they thought this was the best way to design it.

The trigger shows potential, but I obviously don’t know how to make it sing. I hope somebody will take me to school.

Given the complexity of working on the Fusion, I can see why the instructions for these adjustments were left out of the manual. If you are smart enough to find them, I guess you’re qualified to adjust them!

Accuracy is next!