Maximum FPS From QB78 22 Cal. With Minimum Tuning ?

Just wondering what kind of FPS, not FPE, I could expect from a 22 cal. QB78 with minimum tuning ? I know the heavier the pellet the less FPS but just using a medium weight pellet.

Thanks Bill

Bill, Ian again, using Chrissy's account. I took these figures from Chrissy's .22 rifle out of the box.
Weight   FPS   FPE
15.3   420   5.99
22.2   420   8.70
28.5   320   6.48

I have seen them slower but not much quicker when new.

Minimal tuning results are hard to gauge as the result of many of the mods are cumulative.

The poor mans tune is to place a washer or two under the hammer spring but on it's own will not do too much for the performance, 20-30 fps  but will give the valve stem a hard time and guzzle gas.

Opening out the ports and or valve is where you will see the most improvement but I would not call those mods minimal.

Ian

Ian, thanks again for the information.

Looks like you almost doubled the FPE and I guess the FPS with the modifications you made to the QB. Could you tell me what you did ?

Thanks Bill

Bill, the sizes I start with for .22 are in this post,

http://www.gatewaytoairguns.com/airguns/forums/thread-view.asp?tid=913&posts=11&start=1

Also polish the trigger mating surfaces, the hammer, spring, cocking block, all the slots in the tubes, the bolt and chamber.

Bob's article is a very good starting point but personally I have not had to do any valve work as I can get to the UK power limit without needing the effort and it seems to be sensible with the gas too.

Ian ( on Chrissy's account again, not gone home yet :-) )

[mikeiniowa]

Just changing the transfer port seal from the factory installed to an after market one (id.170) will give you about 25fps to 50fps depending on how messed up the factory one is. Installing an extened bolt probe and changing the transfer port seal will give about 50 more fps. Doing both should get you in the 550 to 600 range quite easily. Aligning the port in the barrel with the one in the receiver will give another 10 to 20. Just cleaning and polishing the hammer/cocking block is good for about 10fps. I have one rifle here that is sold that has all that done with no valve work and it's doing about 625 to 650 depending on the pellet and giving about 45 to 50 shots per fill.

[DanoInTx]

Hope all went well on your trip, we sure have missed ya,

Dan

[mikeiniowa]

For a few days anyway, my sister relieved me for the next few. Then it's back to the front.

[mikeiniowa]

The easy way to gain fps with the least work seems to be drilling the entrance port in the probe, you can gain up to 100fps by opening it to about the same size as the exit or a might bigger, I have opened then to .180 inches.