First Top 5 things you'd do to tune a QB78

[dank]

Ha! and you thought you'd find them here.

Nope I'm just asking for a recent consensus from all the knowledgeable folks here . I would do a search but I'm afraid I'd find some past contradictions ie. old news prior to recent modification news.,

 I'd like to find the most up to date starting point mods that exist short of complete valve rebuilds.

Any input appreciated.

N.E.Dan 

[yel01z06]

dan are you talking about a qb-78 or in fact a qb-88?

[dank]

yel01z06 - 4/29/2008  2:27 PM  dan are you talking about a qb-78 or in fact a qb-88?

What do you think  I'm stupid or senile or....um... oh yea QB78  oops 

[yel01z06]

hopefully Mike will chime in and give you a good answer

[mikeiniowa]

first thing is to make sure it has a good barrel, all else is poop if you don't, do a complete tear down and clean every last part with soap and water then give it a shot of WD-40 to remove any water, polish the bolt, hammer, cocking block, the inside of the reciever and cocking slots, polish the inside of the gas tube where the hammer and cocking block run and polish the slots, remove the cotton filter from the valve and clean all the fibers out of the inside, slightly taper and polish the pierceing end of the pin, replace all the seals, properly lube everything and reassemble,( gain of about 10fps) you are now ready to start modifying parts,.....throw old transfer port seal away and install ice maker tubing seal (gain of 20 fps)..increase opening in the bolt probe and inlet hole(gain of up to 40fps), reduce head of piercing pin and taper valvehead (gain of 30fps), open inlet end of valve body(gain of 20fps), install pin type probe in bolt (gain of 40 fps), replace spring in valve with lighter one (gain of 20 fps)...........then set it up for HPA and away you go......

[ribbonstone]

..I'd shoot it a bit as issued (after a good barrel cleaning) to be sure the barrel doesn't have problems....would be a shame to waste time on a clunker barrel.

The three "must do's" would be the transfer port seal...the bolt probe...and an internal smoothing.   If you don't care to replace the bolt probe with a solid wire conversion, can drill the probe inside enough to clean it up (won't enlarge it a whole bunch)...not as much vel., but really not far off.  Cleaning up the inside of the gas tube dose more for not cutting o-rings when you assemble than for speed, but  less friction on the hammer/striker does translate into a bit more power (and  smoother cocking).


BTW: if yoiu really want a clean barrel, then go after it when you have it off the gun.  Can use carb-cleaner or other solvents without worry of getting it inside the valve.

[dank]

thanks all.
in .22 is there any advantage to enlarging the transfer hole in the actual barrel on it's way to the probe, since we've gone through the trouble of insuring the seal was enlarged enough with the fridge tube insuring more air to the pellet?

[dank]

ok, I did the transfer port o=ring, polished the inside plug, hammer,cocking block breach bolt assy and all the edges the various pins slide in.
I of course polished the trigger and also tried to file the end of the breach that accepts the barrel since I tore the inner most o-ring in two during disassembly.

She is wonderful to shoot, Spot on out to 35 yards with practice. 25 she's a nail driver. 10's almost no fun.

I've never chronied this before so you guys tell me if there is more to be had without hurting c02 consumption too much.
Cross .22 pointed 14.9 = 575-600 fps
JSB Exacts 16.2g 485-500 fps.
Normal for this gun?

[PeakChick]

My QB78 list:

1. Buy a Mike Melick, Flying Dragon tuned QB78.

2. Take it out of the box, mount a scope, sight it in, shoot Grackles.

Hey, that's my whole list  ..........  

[yel01z06]

i think peak has it right on the money as usual

[dank]

Thank You Peak Chick.
Wana lend me $200.00? You see I really want an AR.
Never mind I don't like to borrow money!
How about a gift? :emoticon:

[dank]

He Gene? Can you change that 88 to 78 so everybody doesn't have to know just how scenile I am?    :0  :0