QB78D 177 converted to PCP numbers

[sevnandsevn]

Finally finished converting my QB78D 177 to pcp. Pretty happy with the final results.

Transfer port seal and Bolt probe upgrades              Velocity     Ft/lbs
QB78D 177 Gamo Red Fire  CO2  78 F                         659       7.52
QB78D 177 Gamo Red Fire  CO2  88 F                         746       9.65
QB78D 177 @ 1400psi Gamo Red Fire                         854       12.62

Transfer port seal, Bolt probe and Modified valve body
QB78D 177 @ 1400psi Gamo Red Fire                         996       17.16

[WesBob]

Nice job! Did you do a reverse tank or have it sticking forward?

[sevnandsevn]

Sticking forward. I'm using a coil and 90ci bottle right now while I test different pellets.

[WesBob]

Oh ok! Yeah that's easier to deal with for tuning etc.

[nervoustrigger]

Nice workmanship!

A 17fpe .177 makes a nice a 50yd gun well suited for both targets and pest control.

How did you fare in the barrel lottery?  Or have you rebarreled it?

[SwampHunter]

Nice to see the qbs still being built!

[Jayrotx821]

What would be more advantageous, drilling the extra holes in the valve body (silver aluminum part) or cutting that part just past the threads to hold the iring in place (nervoustriggers valve mod). I'm not sure I understand why that mod is done.  I think someone else did the same thing and called it a maxi valve. 

[SwampHunter]

More plenum volume and flow

[nervoustrigger]

x2 on what SwampHunter said.

Eliminating the aluminum shell from the valve is just one of the available strategies for improving flow.  The upside is it requires little to no machining, as compared to some of the other common methods like milling slots down the sides.  The downside of course is that it no longer has the ability to swap back to 12gr CO2 cartridges.
 
In the case of a model QB79, it also helps increase the plenum volume a bit.  Since it’s a tank version, there’s no real downside to speak of.

[SwampHunter]

Oops mine is a 79 lol

[Jayrotx821]

Ok.  Thanks y'all.  Mine is a 79 too.  It's on a bottle . I'm gonna play around with spring preload and then cut the sucker!!!