Just got my first Co2 rifle.

[RCnMo]

Other than the Crosman .357 I got when I was younger, I've never owned a CO2 powered rifle. I brought Trek's (yel01z06) M.M. tuned QB 78 home to make him a shroud and he sent a couple of powerlets home with me. Well, long story short, I let my wife shoot it and she said he couldn't have it back. I had to buy one for myself (her). I'm not going to post any pics because a QB78 is a QB78 and everyone but me had one. Looks like the bore is centered in the barrel and the only blemish I could find was a pressure mark on the left side of the stock. I'm going to tear into it and give it some ice maker tubing and a good polish and probably shim the hammer spring. Eventually, I may make a riser breech and a full length shroud, depending on how well it shoots. If any of you QB owners have some slick tricks up your sleeve and are willing to let them out, I'm all ears.  :emoticon:

[yel01z06]

congratulations Ralph I am sure you (she) will love it this way I know I will get mine back lol

[mikeiniowa]

Open the port in the barrel........if you are swapping the seal you might as well do that at the same time, .170 for a .22 and .155 for a .177, also remove the filter from the valve.........it will fall apart even after one charge they start to go, most of the time the fibers just blow through and don't cause problems but............

[RCnMo]

Took it apart last night and instead of using the ice maker line, I made a fitted seal out of delrin and machined the breech port to a bit bigger dia shelf (.250) with a .1875" port. I haven't done any valve work yet because I have to find a source for non nitrile o-rings when I reassemble it. I gave everything a de burr and polished the sear. I made a new trigger and safety spring out of .015" wire  and gave the trigger spring a brass plunger. That really made it nice. I did the bolt probe mod and shimmed the hammer spring too. Before I did this work, I was getting 615 fps with 7.9g cphp's and now it is doing 720. I plan on doing some valve work after I get the correct o-rings. Thanks Mike, for the filter screen info.

[mikeiniowa]

See Mcmaster- Carr for the o-rings, most use EPMD or urethane.....

[RCnMo]

I picked up some Viton 0-rings today and did a valve mod. I did mine a bit different and I'm now getting 765fps with 7.9grain crosman premier hp's. I don't know what you can squeeze out of one of these things, but so far, I've gotten about 150fps over stock. I lucked out and shot a dime size group at 30 yards with it too! LUCKY! This thing is a blast to shoot just ugly as all get out! I gotta build a new stock for it.

[RCnMo]

I know I'm running this thread through the wringer, but, I did a little bit of porting today and squeezed another 20fps out of it. Over a 20 shot string, low was 778.1 and high was 794.6 with an average velocity of 785.7. It's 71 degrees out and I gave it a minute between shots. I imagine I could break the 800 mark on a warmer day. This thing shoots great too! What max velocity can one expect in .177 (7.9g) on powerlets only.

[gunsup0331]

thanks for the informative posts!
 Pics would be great as well.

[mikeiniowa]

You can break the 800fps barrier easily, could go as high as 850......just start to really eat gas at those speeds.........

[Jaymo]

Congrats. They are great little rifles.  I want mine to hit 850. Mike, how fast can I get my .22 QB78 to go?

[RCnMo]

Played around a bit with the valve and made a conical spring and did some more polishing. Now I'm hitting 830fps consistently at 72 degrees. I imagine it'll do 850 on a hot day. I made an aluminum barrel band and shroud for it to help it with the looks and gave it a gold tooth! (brass cap) I think I'm done tinkering with the innards and eventually stock work and probably bulk fill will be next.

[BigCat1]

Man that thing is looking good! Did your shroud reduce the report much? You must have a good machine shop at hand to make all that cool stuff..............

[RCnMo]

Thanks, my wife approves of it's looks too. I don't think it's any quieter, but it looks kind of cool when the gas blows out the circumference of the barrel when I shoot it.

[Jaymo]

D***** if that isn't sweet.