Reworking the QB78 air rifle's trigger
by Frank (airbuddy3)

The QB 78's trigger is adjustable for sear engagement, pull weight, and over travel. Although somewhat satisfactory in its original form - it can be greatly improved.

Start by removing the action from the stock: undo the knurled nut in the forearm and put the safety to the safe position. Using a non-marring punch (such as a wooden dowel), push the safety out from the trigger unit frame. The trigger is a modular unit and comes out in one unit after removeing the two screws that hold it onto the tube.

Next, remove the side plate of the trigger unit by removing the two Phillps screws and pulling the plate off the unit frame. Clean and degrease the trigger parts. If necessary, stone the sear surfaces using an Arkansas Hard stone or 400 grit emery. A stone will keep things more square and is the recommended tool. Just polish the surfaces lightly.

Mix some moly and gun oil (50% of each) and using an artist's brush - apply the mixture to the sear, pins, and springs. Be sure to move the parts to ensure adequate lubing. Repeat the oil /moly mix application, followed by an application of pure Moly to the top of the sear and the exposed part of the hammer. Reinstall the side plate and the two Phillips screws.

Looking at the trigger unit, you will notice there are 3 screws used for adjustments:
    1. the large screw at the bottom - is for pull weight. Unscrew it 2 turns and test the feel of the trigger (it should be about 1
        lb.. however, you can adjust it to your liking).
    2. the middle screw - is for overtravel. Screw all the way in to eliminate all the creep.
    3. the top screw is for sear engagement and compensation of future wear. DO NOT ADJUST AT THIS TIME. I dont know how long wear will take, as the parts are very hard and with the molly it should be a very long time.

The trigger unit now has the pull weight screw (screw #1) protruding about 2 mm. You will need to use a wood file to fit the trigger unit in place in the stock. Remove about 2 mm of wood from the stock where the rear of the trigger unit fits.

Reassemble rifle. After the above actions, the trigger is now a crisp 1 lb with no creep and very predictable.

Enjoy !

Frank (airbuddy3)