QB78 Tune
Trigger tune
After spending 250 euros on bulk filling my .177 QB78 (110 euros) I decided to strip and tune the trigger mechanism as best I could. As standard, the trigger is heavy, long in the pull and scratchy in operation. This is a very simple job to do and takes about an hour if you have the tools handy.
The Victim
I started off by removing the safety catch, this must be done as you can't remove the stock otherwise, simply turn the catch to 'S' then push it out from the other side with a screwdriver or centre punch or similar. Then unscrew the big nut holding the action to the stock.
The internals
A = Screw, B = Screw, C = Trigger adjusting screw, D = Return screw, E = Trigger spring, F = Trigger, G = Release sear, H = Safety catch
Remove the stock from the action, then unscrew the 2 small cross head screws that hold the plate onto the trigger block. You will then see the internals as in the above photograph. Don't worry, nothing will jump out when you remove the cover There are only 2 sprung things in there, one is the trigger spring (E) which simply sits in a hole, and the other is a spring wire, holding down the sear (G)
Using a small screwdriver, carefully prise up the trigger blade off it's peg, it should just pull right up and off. Now while you're at it, using a screwdriver, undo screws A and B a bit, no need to take them out, just loosen them. Then using either your nail or a small screwdriver, carefully and slowly release the sprung wire that holds the sear G down on it's peg. You will end up with this below. Please excuse the millions of white dots......they are splashes of T-cut which spun off my polishing mop on my Dremel.......oops!
To pull the sear G up off it's peg is not possible until the 2 screws A and B are slackened off, then it comes right off. The photo below shows which Dremel mop I used
Here is a photo of the trigger sear as it was removed from the gun
First of all, using fine grit wet and dry, I polished the sear faces to get rid of the rough surfaces. It only takes a minute or two by hand. Then when they felt smooth, I used the Dremel polishing mop dipped in T-cut.....perhaps I should have used less T-cut, as soon as I turned the Dremel on, everything within 6 feet was spotted....ah well. This is the result below.
I actually smoothed and polished all the touching surfaces I could see. I then replaced the trigger and sear back into the block, greasing with high melting point grease. The photo shows an excess of grease, I actually cleaned a lot of it off. Before replacing the metal plate. There are three adjusting screws, C, D and E which determine how the trigger operates. C adjusts the 2 sears, giving a sharp release when screwed in, D is merely a back stop screw and E is the trigger pressure adjuster and spring. Be careful when adjusting C, you don't want a hair trigger as in a match gun because the looseness of the QB trigger mechanism means it could fire when you don't want it to......
My QB78 is now fully fettled, both trigger wise and also the action has been done. Unfortunately, I forgot to take photo's when doing this so might just have to obtain another 78.....any excuse
