Air Gun Home :: View topic - QB-78 HPA tuned ....

Gunrunner · Member

I think I'm getting pretty close in the fine tuning of this QB-78. with ajustable hammer.
Here is the latest shot string using crs. hollow 22 cal. with 2700 psi and there was 1600 psi remaining at the end of the string ..
1 -915
2 -912
3 -918
4 -921
5 -920
6 -926
7 -924
8 -928
9 -927
10 -930
11 -932
12 -931
13 -937
14 -942
15 -940
16 -944
17 -942
18 -950
19 -956
20 -955
21 -951
22 -948
23 -953
24 -947
25 -939
26 -933
27 -923
28 -915
29 -894

The next thing I'll do is fill in the hole in the hammer where the spring guide goes to make the hammer heavier and maybe more consistant shots.
Pretty happy with it right now and with 1600 psi left it takes no time to pump it up again..
So how does it compare with other QB-78 hpa's and B-50 and 51's ..
please post .. like to see a comparison ..

Gunrunner

AirGunEric · Site Admin

Nice numbers. Another 100fps and you can hear it break the sound barrier. Wink

If you don't mind me asking- what did you do to get the valve assembly to remain stable at 2700psi of pressure trying to push against it?

Any idea what kind of money it took to get it in the 950fps range?

And lastly- are you using a scuba tank to fill it, or a hand pump? If a hand pump- how many pumps does it take to fill the reservoir in the QB? Also- what size is that reservoir?

StevieLaner7777 · Moderator

SWEET

Those are some nice figures.
That Rifle is very very well tuned to get almost the speed of sound with .22cal pellets, looks realy nice too.

How accurate is the rifle? and what is its max accurate range?

Stevie Thumb Up!

StevieLaner7777 · Moderator

Just a few questions on mach 1 Crazy/Loopy

I do know a bit about the speed of sound as I'm in to Aircraft and physics, But I just want to know a little bit more about it from the AirGuners point of view, So here are a few questions for anyone to answer or share their opinion on.

How fast is the speed of sound exactly in FPS?

I hear that breaking the sound barrier can affect accuracy, Is this ture?

Can the sonic crack be silenced?

Can a regular silencer handle sonic ammunition?

I also know that all aircraft that can exceed mach 1 have to stay sub sonic over land as this sonic boom can cause window to break, farm animals to go crazy and even cause avalanches, So why doesn't the sonic crack from a fire arm do the same? Is it a Mass thing or something else?

Any knowladge or awnsweres will be greatly appreiciated.

Stevie7777 Thumb Up!

AirGunEric · Site Admin

Gunrunner · Member

the the 2 screws with higher grade machine screws, the one holding the valve and the one holding the breech down which also holds the back stop for the valve, the 3rd screw that goes into the back stop and holds the stock on is the same one.
The most I got out of it was 1043 and that was with a bigger brass transfer port .. not very efficient at all, figure the sweet spot is around 925 to 950 with still plenty of power to hunt and with 30 shots I don't even have to take my Hill pump with me.
The tube is .880 O/D the wall thickness is twice as thick is the standard QB and the volume I have no idea.. sorry, the length of the tube is 26" same as the QB with the extend a tube. Never really counted how many pumps, from empty it takes about 10min of pumping at a slower pace and 5 min from 1600 psi. not bad really, I find from 2700 to 3000 psi I really have to lean on the pump .. so I just for go the last 300 psi.
I got to say from day one when I bought it from Sniper this QB has hit the mark ever time, its got one sweet barrel and after I converted it, its still hitting dead on.. I got it into the low 700's with Co2 and 50 yrdswas pretty standard .. I haven't had the chance to really do any long range target shooting yet .. but as soon as I do I'll post it.
If anybody is interested I sell the tubes for 175.00 canadian. with ajustable hammers 200.00.
Eric you were asking how much, with a used Hill pump, cost me 575.00

Thanks
Gunrunner Cool

Gunrunner · Member

breech hold down..

Gunrunner Cool

AdrianM · New Member

Where can I find all the mods necessary to increase the power of my QB78?

I don't mind searching...just point me in the right direction.

I am a machinist and I would like to get to work on my rifle.

AirGunEric · Site Admin

Gunrunner and leadman are the ones here who know the most about the QB-78's and mods to them. If you caught it- Gunrunner's main modification was converting the gun from Co2 to pre-charged pneumatic (compressed air) and then driving 2700psi through it. The most significant mod to doing this is replacing the tube/tank assembly that holds the dual Co2 cartridges with one that can handle 2700-3000psi. Aftermarket parts like this are available- I just don't know who specifically sells them offhand. The other main requirement for converting to air is modding the valve so that it doesn't lock up with that sort of pressure.

Hopefully either Gunrunner or leadman will come around and throw some more info in here.

23ib0d0n · Moderator

metal tube
http://www.mcmaster.com/

AirGunEric · Site Admin

Here's a list of the "essential" modifications to a QB-78 from airgunartisans:

http://www.airgunartisans.com/flyingdragon/tips.html

Other mods involve increasing the size of the transfer port and replacing its seal with poly-tube like what is often done on a Crosman 22xx gun in order to reduce restriction of gas flow (Co2 or air- doesn't matter which).

And in case you missed it, leadman's trigger tune:

http://www.airgunhome.com/agforum/viewtopic.php?t=357

-which won't gain you any power, but will make shooting the gun that much more enjoyable.

Alstone · Moderator & Site Supporter

leadman · Veteran Member

http://charliedatuna.com/CO2TuneByCharlie.htm

QB mods

those are the ones that i used, i dont recomend modding the valve unless you know exactly what you are doing or happen to have a spare on hand

hope this helps

Eric