Another QB78 Project

[remtom1200]

IMG_0653.jpg
New custom trigger and bought a new scope from Scopes and Ammo. Also shortened the bolt handle a bit. Took a few shots over the chrono and was surprised 680fps average 10 shots at 850psi. Very curious now what it will do at 1600psi.

[sholo]

Lookin' good!!

What is the parallax set at on your scope?

Todd

[remtom1200]

I am not sure what the parallax is set at. Lets ask Eric to see if he knows.

[rsterne]

I guessed that the average velocity is 685 fps, which works out to 18.9 FPE times 20 shots is 377 FPE.... I assume a 13 CI tank times a 70 bar drop is 910 CI or air used.... That works out to only 0.41 FPE/CI, which at that power level, frankly, is dismal.... I'm guessing the hammer and spring are stock, and as such are optimized for about 1200 psi or more.... Regardless of whether that is the case or not, you must have wayyyyyyyy too much hammer strike for the pressure you are running, hence the monsterous air use.... Since you are planning a big increase in pressure, I wouldn't worry about it, and in fact you may have to increase the hammer strike over stock to run 1800 psi.... I just thought you might like an idea of what is happening....

Bob

[AirGunEric]

Sure- ask the guy who can't remember his own name half the time... What model was it again?

Ha ha. SEFFR3940R- I believe it's parallax is set at 20 metres (might be 15m, it's been awhile since I paid attention to that model).

[remtom1200]

Ahh yes, my custom trigger

[SeanMP]

Here is a quick little vid on flame hardening or "direct hardening" with a propane torch

http://youtu.be/A8OlmtwnpVI

1144 or "stressproof" is the ideal material for the small shop. It is a pleasure to machine. Slightly stronger than chrome moly. Medium carbon, resulferized.Once you have used it you will never buy another piece of 1018 cold roll.

[SeanMP]

It does sound like the balance is upset. How much of a major haircut did you give it? Any idea how much the weight has changed?

Try a viscous dampener by sliding an Oring on the spring guide. This wont affect output but will upset the harmonic somewhat. Works better if you have a continuous guide and a tight fitting Oring on both ends of the spring. Takes the bounce out of the boingy-est springs

[remtom1200]

I will take some pictures after the two stage plunger is made and installed.

[rsterne]

Excellent video.... I thought the part looked hotter (more yellow) than what I usually do, but that could be the colour balance on the camera?.... I guess as long as it's no longer magnetic, it's hot enough?.... I've never heard of 1144.... nor any idea where to get it.... I have some 1045, and of course O1 drill rod.... any significant difference?....

Bob