Canadian Airgun Forum

My Ampell Acro1 had always missed the seal for the CO2 cartridge. In the past, without having to disassemble anything, I solved the problem with o-rings and the smooth plastic of a coffee can lid but since I now have a good supply of Delrin I decided to revisit it to see if I can get a better solution.

I have to say that the pistol was not leaking but since it is old I thought it might be a good idea to do a complete resealing job.

The information on the Ampell Acro1 is fairly scarce but on the Classic Airgun Pistols Association website I was able to find a picture showing that its guts are fairly simple.

After taking it apart I also discovered why I had a problem with the trigger return. A spring was missing and, I don’t remember how I manage to find the information on the web but I came across a video covering exactly that topic. It seems that the Acro1 uses a torsion spring (the one with two legs) but after looking in my box I didn’t find any suitable candidate. I thought I could quickly make one with a piece of spring wire (which, in retrospect, turned out to be a bad idea since I poked myself through my index finger). I then decided that a small compression spring would do the job as well as the other type.

From my experience it seems that the Acro1 is one of the simplest CO2 airguns to work on. After the side plate is removed only a few components are discovered. There are the barrel assembly, the valve assembly, the hammer with its spring plus the cocking button and finally the trigger. Basically there should have been a trigger spring but it was missing.



The valve assembly is very simple too. I am not sure why they use a rolled spring steel pin but, again, I had to fight with it to get it out. I am planning to use a plain pin when I reassemble it because when both sides of the casing are screwed together it has nowhere to go.

The valve has five components: the valve body, a spring, the valve stem and a plug with a seal. The stem goes through the seal and the plug (in which the transfer port and locking groove are machined). The seal is a tight fit in the valve body and requires some persuasion to get out. Carefully clamping the valve stem end in my machinist vise helped to get some leverage.



I made the seal with Delrin and checked the fit against the valve body frequently. I also machined a jig to be able to warm up the seal and hit it against the valve stem cup with a hammer to imprint the edge.
What I didn’t realize was that the nice tight fit I had patiently worked for on the lathe would be definitely altered after being smacked with the hammer. It had expanded enough to be a press fit instead.

Since I wanted to be able to disassemble the valve later if needed, this was not acceptable. I started to file the periphery of the seal to reduce its diameter enough to go in and out of the valve body without getting permanently stuck in it when I was checking for fit. It took me a while, but it worked.

The seal was covered with a thin coat of silicone grease and a few drops of Pellgun oil were added in the valve body before reassembly.

Now that the valve was taken care of, it was time to look at the CO2 seal. I machined one from Delrin but because it is very hard I discovered that the cartridge cannot be inserted. Since my original fix was working I decided to keep it as it was and reinstalled both o-ring and the two layers of plastic.



The small o-ring seals around the piercing pin and fits inside the larger o-ring which, in turn, seals the cavity. The plastic from the coffee can cover provides the bridging to distribute the pressure on both o-rings. As the plastic is also pliable the tip of the cartridge has no problem to seal against it.

The airgun was pressurized and it was holding. After shooting it empty, a second CO2 cartridge was installed and the pistol was stored overnight. The day after, it was shooting normally so I consider that it is a successful resealing job.

R-Gun Pete