Smoothing the Air-Pistol Trigger Mechanism

Some air pistols are cheap and are not worth fixing, while others—the high-dollar units in the $800 to $1,500 range—might require expertise that is beyond most gunsmiths’ training and experience. In the case of the big-ticket air guns, you might want to suggest that the owner return it to the factory for repair or adjustment. On the medium-priced air pistols, however, the work can be relatively quick, and can help to create anew customer base.

When it came to fixing the Gamo Compact shown here, I decided it was worth the effort, even though I hadn’t previously included work on air guns as apart of my gunsmithing repertoire. That’s because this problem was a personal one. After firing approximately 40,000 pellets from my Gamo Compact air pistol, the match-quality trigger began to fluc tuate between a light let-off and an unbelievably hard one.

For a moderately priced, extremely accurate pistol that I’d grown quite fond of over the last decade, this was unacceptable. Of course, I could have returned the gun to Gamo, USA, but what fun would that have been? The first thing I did was document the problem, just to ensure it was the gun and not just my imagination. Using an RCBS trigger-pull gauge, I fired the pistol a total of five rounds.

The first pull tripped at 2.5 pounds, the second at 3.9, the third at 2.1, the fourth at a whopping 9.0 pounds, and the fifth was 2.5. It was not my imagination. Now, all I needed was a diagram and some time to work on it. Finding the time wasn’t as difficult as finding the diagram. I’m sure somewhere there is an honest engineering diagram; unfortunately, it isn’t available to you or me. After repeated tries on the internet and attempts to cajole one from Gamo, USA, I gave up and made the diagram you see here.

It’s not down to the internal valving, because my problem didn’t go that far. So here’s the procedure I came up with for doing a simple action job: First, open the breech enough to ensure there’s no pellet loaded. After making sure it’s uncocked and empty, carefully remove the target grips usually found on the gun. Be certain you use an appropriate Phillips head. (I used the smaller of the two in my

Chapman set.) And don’t bugger up the screw heads. Remember, these seemingly crudely finished grips are currently running around $60 to $95 a set. You have to watch the tiny washers (two each, top and bottom), two in each panel. Lose those, and you’ll wish you had 20/400 vision. Those washers are threaded, too. Carefully set the grip halves to one side of your workbench. Next, again using the proper-sized Phillips head, carefully remove the three action-cover screws from the grip frame.

Keep these screws ordered with their mating holes—they’re not interchangeable. Pry the action cover off carefully, because there are action pins fitting into it from the opposite frame panel. It might be best here to replace the screws in their appropriate holes in the cover after you’ve removed it and set those aside with the grips. Again, a word of caution: The cover is a hard plastic, so be gentle, especially if it’s become brittle with age.

After you’ve removed the cover, take a moment to familiarize yourself with the order of things. Check it against Figure 1. If it’s different, it may be newer or older than the model l have. You’ll have to make sure you have an idea how it all works together. My gun was greased up with some lubricant of an unknown origin.

Before you use any solvent or lubricant on this or any other air gun, cut a small piece of the plastic from the inside of the frame (where it won’t show), and place it in a little lubricant or solvent overnight. If, the next day, you see a plastic puddle, don’t use it on the gun! A great many lubricants and solvents you can use on a firearm with impunity will quickly destroy a costly air gun. At the very least, it will destroy the seals and O-rings.

I first took a cotton swab, dipped it in isopropyl alcohol, shook off the excess, and gently cleaned the gook away from the working parts. This gave me a clear view of the working mechanism. The hammer, mainspring, trigger, sear, and sear-return spring were clearly visible. The pins holding it all in place were freed from the drag of hardened grease, too. Using a pair of jeweler’s needle-nosed pliers, carefully unhook the mainspring and trigger-return springs from their posts/pins to which they’re anchored.

Next, carefully unhinge them from their respective components. Place them in a bath of alcohol (or use your wife’s ultrasonic jewelry cleaner) for a few minutes. Set them aside to dry; we’ll get back to them later. Next, gently work the trigger and hammer pins loose from those pieces through the left side of the frame. Carefully remove them from the frame. Notice both the sear piece and the hammer are of a white metal, and several pieces are riveted together to form one working piece each.

I don’t know why Gamo did this, unless it was to save money. If it were made by Umarex, the German parent of Wal-ther, it would probably be a onepiece steel unit. In any case, observe how the wear marks are worn in the sear and hammer. It’s best to clean them gently with the same alcohol bath you used on the springs before going further. Stone those areas very lightly in the direction of wear with your hardest Arkansas stone. Since these pieces are probably aluminum or a zinc alloy, their softness is a given.

Be sure to use a light honing oil as you stone the surfaces, and make sure you clean the pieces as thoroughly as possible when you finish. The slightest amount of grit left will cause an inordinate amount of wear, and will possibly work its way up to a seal, ruining it, too. You can never clean a stoned piece too thoroughly. After you’ve stoned and cleaned the sear and hammer, lubricate the sear surfaces with either White Lightning (the lube, not the hooch) or dry, powdered graphite.

This way, the lubrication will not attract the grit and Figure 1. grime of normal oiling. Place a small dab of spring gel on the left side of the pinhole in the sear and hammer. When you replace the hammer and sear pins (from the left side of the frame where you removed them), you’ll distribute the lubricant through the hole as the pin goes through. Now, let’s return to those two springs we cleaned and set aside.

Using spring-dampening gel on a toothpick or dental tool, thinly coat the coils of both springs and apply a very small amount to the holes in which each spring is inserted into both the hammer and sear. Insert the sear spring first and attach it to its post on the frame. Next, insert the hammer spring and attach it to its frame post. Finally, replace the action cover, gently working the cover until the sear and hammer springs seat in their respective holes in the cover.

Replace the screws and grips, and you’re ready to shoot what will feel like a brand new air gun! Checking with the trigger-pull gage, five shots were within .1 pounds of a 2.5-pound pull. You can’t ask for more than that. The type of metal used means the process will probably have to be repeated in the future, and I don’t guarantee it will last for years if you shoot a great deal. But you now know how to do the job, and it’s not that difficult. Perhaps someone knows how to "harden" these surfaces.

If you do, please share. ■