Max speed for CO2 powered QB78/9?

[GuyFromTheWoods]

Hey guys, I was just wondering what the typical max speed is for a qb 79 modded completely out. I currently get 693 fps with 14.3 gr crosman premiers. I haven't tried my 18.1 JSB exacts yet, but I will. When I first got the gun, it only shot about 440ish. Now, after opening the transfer port, bolt probe mod, valve mod, trimming rough edges and polish, and hammer spacing by .25 inch, I get that 693. I dont feel that I can really complain considering I got a 250 fps jump from stock, but I would like to know if I there is even a point to keep modding to increase speed with CO2. Ill switch over to PCP eventually, but not wanting to dump the money on a pump right now. I figure Ill make a teflon valve soon as I get around to getting the material, as well as a finer polish and spring tension adjustments. Your expertise is much appreciated.

Equipment
QB79-slightly modded
JT 90 gram prefilled tank
Leapers 4-16x50 mildot

[wilsonj1018]

Before I went hpa with the one I had after a huge amount of work I seem to remember 20 fpe in .22 I converted it to 177 soon after hpa
Josh

[rsterne]

It all depends on the temperature.... 700 is pretty decent at 70*F, you aren't likely to find much more.... Most of the claims I have seen for higher are at higher temperatures....

Bob

[GuyFromTheWoods]

It all depends on the temperature.... 700 is pretty decent at 70*F, you aren't likely to find much more.... Most of the claims I have seen for higher are at higher temperatures....

Bob

Im shooting at about 70....Im inside the house . I turn all the lights off with 4 sheets of cardstock taped together and thrown over the chrono. Turn a 4 four foot flourecent light upside down and lay it right next to the chrono and wallah, it works! But i need to test it outside to make sure Im getting an accurate reading. All the shots were pretty close though...

[rsterne]

Fluorescent lights will cause a Chrony error as they "blink".... you have to use incandescent lighting (or ones that don't blink like LED running on DC), two sources, one above each sensor.... a single source will give high readings.... Your reflective cardstock MAY work like a "sky" or may not, but you can't get away from the blinking of the fluorescent tube....

Bob

[GuyFromTheWoods]

Fluorescent lights will cause a Chrony error as they "blink".... you have to use incandescent lighting (or ones that don't blink like LED running on DC), two sources, one above each sensor.... a single source will give high readings.... Your reflective cardstock MAY work like a "sky" or may not, but you can't get away from the blinking of the fluorescent tube....

Bob

Im not arguing here (Im really new at this chrono thing, less than a week into it), but are you meaning it wont work period, or it wont work correctly? I got fairly consistent reads and only got ERR messages if I shot too high. Im currently planning on making a light weight box that will attach to each of the diffusers with an incandescent bulb inside. Probably just cardboard, tape, and a hole in the top with the wires coming through it. I tried DC LED lights, but no luck.

[rsterne]

Take your pick.... in your case it's obviously working for you if you are getting consistent readings.... I have tried a Chrony in a room with fluorescents, and got wildly inaccurate readings and lots of ERR messages.... That is very common....

Bob

[GuyFromTheWoods]

Take your pick.... in your case it's obviously working for you if you are getting consistent readings.... I have tried a Chrony in a room with fluorescents, and got wildly inaccurate readings and lots of ERR messages.... That is very common....

Bob

Is it possible that the card stock somehow reduces the flicker to an extent that works with the chrono? Ive tried incans and fluors and neither worked if place above. The only thing so far that has worked is a fluor set up so that only reflected light is received by chrono, and sunlight if there is cloud cover.

[rsterne]

Incandescent lights are the best indoors.... but you need two, one over each diffuser.... A single light source, even with the diffusers, will make the Chrony read high....

Bob

[Acapulco]

Congrats on the 79. I bought mine years ago and modded mine too.  693 fps with 14.3 gr crosman premiers is running a little fast. (wasting gas) Dial her in around 650 and you'll be go to go.

You must be new...you're looking for speed. Remember speed doesn't count, only accuracy.

Also,  order some JSB's.... Good luck

[GuyFromTheWoods]

Congrats on the 79. I bought mine years ago and modded mine too.  693 fps with 14.3 gr crosman premiers is running a little fast. (wasting gas) Dial her in around 650 and you'll be go to go.

You must be new...you're looking for speed. Remember speed doesn't count, only accuracy.

Also,  order some JSB's.... Good luck

Hehe, I may be new, but I understand the basics of what is really important . However, I like to see how fast I can go before I get down to what really matters. Explained in a different sense, if I get a new Dodge Cummins, Im gonna make it be the most powerful truck around, but when i get done playing, Ill tune it down and make it to last for thousands of miles of towing cattle and general farm work.

That being said, I dont know if ladder testing and such applies to airguns, but I figure I might try it. I do so with my 308 to find the most accurate load nodes and then fine tune from there. Im brand new to this precharged CO2/HPA thing, so Im open to advice.

Taking out the hammer spacer didnt slow it down any...what now? When I modified the valve, I actually increased spring tension because I was getting some leakage into the breech/barrel. Therefore, am I wasting air, or just using it more efficiently? Im confused to why taking out that spacer didn't help me more...until I am running HPA, Id rather not be wasting air. 90 gram CO2 is 12 bucks for a two pack at wally world. Id buy a large tank and get it refilled, but the cost savings probably wont pay for itself by the time I get HPA. Thanks for your help/advice!

[rsterne]

Having more hammer strike than you need only wastes CO2.... That is likely what you did when you added the spacer.... so removing it kept the same velocity and saved you some CO2....

Bob

[Ribbonstone]

That extra striker spring tension might be handy at about 90F, but at the temp/pressure you are shooting, (so far as the pellet is concerned) it's just squirting out co2 after the fact.

Not opposed to a teflon/Derin valve stem seal.  Can add speed, but more important is that it less likely to get chewed up by the dirty quailty of co2.  Co2, bulk fill or tanker, just isn't all that clean.

[GuyFromTheWoods]

Having more hammer strike than you need only wastes CO2.... That is likely what you did when you added the spacer.... so removing it kept the same velocity and saved you some CO2....

Bob

Oh, that makes sense...I dont know why I didnt think of that. Thanks!