Author Topic: Tuned my QB-79 over the weekend  (Read 2912 times)

Offline SDale

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Tuned my QB-79 over the weekend
« on: August 05, 2008, 03:05:09 AM »
With GREAT results!!!

In short, I did EVERYTHING listed on the CDT COtune and added a couple of my own touches.  After porting, I polished every spot to a mirror shine where CO2 would pass through, enlarged every port as large as possible without causing problems. The hammer got a nice polish with 1000g wet sand paper and a couple shims added.

After 5 hours of careful dilligent work, she's shooting a little under 700 FPS at 73 degrees. But now there's a problem..... She's LOUD!!! Sounds almost like I'm shooting a rimfire hehe!

Offline Splash

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RE: Tuned my QB-79 over the weekend
« Reply #1 on: August 05, 2008, 03:12:41 AM »
Sounds like she turned out nice Sam. I've got new valve in route for mine, hopefully I'll get it right this time.
Mike
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Offline SDale

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RE: Tuned my QB-79 over the weekend
« Reply #2 on: August 05, 2008, 03:15:31 AM »
Had to order a new one for mine too!!! I actually started the tune last week, but when I tapered the valve stem, I sort of cooked the seal. This time around I used a "Misty Mate" as a mist cooler on the lathe. Worked great!

Offline ribbonstone

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RE: Tuned my QB-79 over the weekend
« Reply #3 on: August 05, 2008, 11:05:06 AM »
it's fun, in a strange kind of way, to get the rifle shooting to your desired vel.  that's part of the fun of Qb's: the ability to "tune-n-tweak" the rifle to shoot how you've put your mind to making it.

A suggestion that may not go over well; we all get the "need for speed". Think about backing it down to 650--660fps (in .22 I assume).  At that speed using good pellets (Crosman Preimers or Benjamin Black Tin Diabolos)  will have about 500fps/8 foot pounds left at 50yards.  That's enough to do in any squirrel or rabbitif the pellet lands in a spot to intersect the "good stuff" inside.

For giving up that 50fps (and about 4/10ths inch drop at 50yards) will get a smoother cycling, easier to cock, somewhat quieter, longer shot string rifle...it will still work fine out to the 50yard/1" group distance QB's seem to limit out at....and is a lot friendlier rifle to operate.

For the noise, either live with it or look up one of the custom brake/shroud makers.
Robert

Offline SDale

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RE: Tuned my QB-79 over the weekend
« Reply #4 on: August 06, 2008, 02:21:37 AM »
Thanks for the tip ribb!!!

After the tune, I wanted to tune it back a bit anyway. I'm getting a bit of Snow out of the barrel. Well, not snow but a nice white plume of gas. From my paintball days, that tells me "TOO MUCH GAS!!!". She's smooooooth as silk though!

As far as quieting her down...I've already got sum'm in the works! hehe  8)