Author Topic: First time QB78 tuner, aka QBInTx  (Read 4300 times)

Offline DanoInTx

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First time QB78 tuner, aka QBInTx
« on: August 30, 2006, 11:28:44 PM »
Got my first QB a few days ago. It was given to me by Joel Lively at in trade for....well not really in trade, but I gave him my B30 that I knew he would want. He told me that it wouldn't hold air, but if I wanted to I could try playing around with it, so I took him up on his offer. The QB in question looked pretty much bone stock, like it just came out of the box, except of course that it wouldn't hold air, so I did what any good airgun nut would do...cleared off a space on my workbench and took it all apart!

I first went to Bob's website as I had seen a tune guide there in the past for the QB, and found it here:

The guide was really easy to follow, and I had no real problems getting this thing apart, except that I didn't have any small metric allen wrenches...doh! After a trip to Ace I began disassembly, which took me on a trip back to Ace for a screw extractor. It seems that the tiny allen set screw that holds the bolt handle to the bolt was already's an M5 setscrew if anyone is wondering, but a 10-32 is a pretty close match also. I didn't do the full tune that Bob has outlined as I plan on having this thing apart again in the future, I just went for the meat of it. Here's a list of what I did:

1) Opened up the bolt probe hole by a 1/16th or so
2) Also opened up the bolt probe port on the bottom to the same size as the hole in the bottom of the barrel(which I also opened up by about 1/16th")
3) Opened up the valve exhaust hole by the same as the barrel and probe port holes.
4) I tapered the valve stem a wee bit(down to 5/16" as suggested in the guide) as well as the piercing pin.
5) Drilled 4 new holes in the valve body to get more air into the valve from the CO2 tube.
6) Deburred the barrel and the breach so it wont eat barrel o-rings anymore
7) Sprayed everything during assembly with silicone spray.
 Reassembled the trigger with moly+30W motor oil mix
9) Replaced trigger return spring with a slightly longer, but much weaker spring(someone else had already chopped the stock spring a hair, so I went with longer/weaker wire).
10) Adjusted the trigger so there is about 1/16th" of travel before the gun fires, then hits the stop right after that...very light, very little travel!
11) Cleaned all Chinese "gunk" off of everything with brake cleaning fluid.
12) Chucked the bolt handle up in my drill press and cleaned it up to remove tools marks with a file and then polished it up with some 400grit paper...for looks and bling factor!

I used standard faucet o-rings as replacements, which I know don't mix with CO2, but this was a trial run, I plan to have it apart again and I really wanted to shoot it. I also didn't polish the trigger surfaces as they looked pretty clean as-is, but I did lube them up a bit and suspect the next time I have it apart I'll do these tunes also. Actually even with my limited trigger tune/adjustment this thing has a really good trigger...or good compared to most everything else I shoot.


I own no chrony, and I didn't shoot this before the tune as it wouldn't hold air, but I have shot what I believe was a stock .177 QB78 and I can say that this shoots MUCH harder..., but it's a .22 so that would make a difference. It'll bury a pellet into a 2x4 far enough to where I can't see the pellet skirt...plenty hard enough. Shots per fill???? I dunno as I haven't run the first two carts dry yet, but I'm guessing not many

I have a scope I plan to put on this thing next to see how it'll group, after that it needs wood. I think Steve Corcoran at knows what wood this needs. After that all I'll need is a muzzle brake and alot of CO2 and I'll be set for awhile. I find this gun to be a little smallish, like youth sized, so a little work will be needed here. Here's some pics, I think it's about the right size for this guy almost:

 Okay, maybe in a few more years
It's a really nice little gun with some work.  I'd be interested in seeing what some of the pro tuners can get these things to do, I'm guessing they can make them amazing.

Yup, for $75-$100 I can see why these have a huge cult following, I want like 100 more of them, these things are fun!


Current shooters: Beeman HW97K .177 with Hawke Eclipse 4x16x50SFAO and Steve C. stock, Beeman R9 .177 with Hawke Airmax 4-12x40AO and Gene\'s Midas touch, Air Arms S200 with Bushnell Banner 6x24x40AO Rowan brass bling and Steve C. custom stock, BAM B25, BAM B40 .177 with BSA 3x12x44AO, Benjamin Marauder .22, Benjamin 397 pumper.

\"repeat this mantra:
Air gunzzzzzz, air gunzzzzzz, air gunzzzzzzz!!!  ...You will feel better\" T.E.C.2008

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« Reply #1 on: December 19, 2006, 02:39:02 PM »