GTA
PCP - HPA - C02 Gate => QB-7X Gate -W/Co2 & HPA => : August 09, 2007, 05:53:12 AM
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I decided to do some playin around with the hammer spring and shims a few days ago. Some might find it interesting some might not...
The shims were the size cdt talked about in his co2 tune.
No shim and stock hammer spring 14.5 grain 680 fps 35 shots
1 shim and stock spring 14.5 grain 710-715 fps 28 shots
2 shims and stock spring 14.5 grain 728 fps and about 20-25 shots max
Just a tib bit of info to share. It really waisted ALOT of gas with the 2 shims and was LOUD as all getout. Even with the "muzzle break" installed it still had quite a puff out the muzzle and a decent report.
Jason
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Jason,
If you open out the transfer port, swap the seal for poly tube and either bore out or probe the bolt you will do better than just shimming the spring!!
Ian
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I have all that done arleady.. Its one of mike m's guns. I was just playing around with it and deided to try it out.
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Hmmmm Pity MM aint around at the mo, he could tell us what he had done to it but I would expect higher than that. more like 800-850 with a good porting
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Is that 800-850 in .177 or .22 cal? maybe I forgot to mention that this was a .22.
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.22. What is .177? ;-)
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Hang on, let me check my history files, I may b confusing CO2 and PCP stats here. I know PCP full on will top 1000 fps in a .22 qb
What I should also have said, rather than hammering the hell out of the valve stem, put a lighter return spring inside the valve, easier to cock than a shimmed hammer too
Ian
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haha yep this is a .22 :-) and runnin on co2 also..
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I wouldnt mind going hpa but not shure which tank and regulator to get. 1000 fps would be insane in this lil qb
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Jason. this is self contained pcp, no external tanks. Charge the replaced gas tube to 170 bar :-)) and they will do over 1000 fps, for about 7 shots!
Ian
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Hello Ian.
What material and size of material did you replace the gas tube with? Did you use something like 4130 steel, what OD and wall thickness, that type of thing.
Thanks
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I am thinking some seamless SS T304 would prolly work.....
John
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Here is a link some my find interesting, saves running a spreadsheet.
http://www.rathgibson.com/tech_info/burst_pressure.asp
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Alot of lt depends on what kind of tune you had Mike do Jason. Mike does a heck of a valve job on them. One thing for sure... when you press them for velocity, they do start to gobble up the fuel..just like a race car. And if you see the "cloud", it's to rich anyhow. The more power, the more fuel. :D Also, the temp has a lot to do with velocity as well as fuel consumption. And Ian is right about hammering the hell out of the valve stem. That is just an easy and simple way to gain but not necessarily the best when there other options and if the mechanical ability is there.
The "D" model that I just had Mike do for me is right at where you are and to me that's perfect, and it ain't a gas guzzler.... in fact, pretty economical and yet has enough power for most small game with good placement. And it is a tack driver for sure.
If you do all of the mods in the CoTune guide, it will be up there but to me isn't worth it. That's why there are so many variables to choose from. It's a matter of choosing or making the right selection of mods for the performance that you want. Some guys don't care and it might not be to bad if it were on the "T" model using 9 ounce tank or any thing else that is bulked and can stretch the shooting time but that of course doesn't cut the consumption.
I've been tossing around the HPA also. In fact Tim was over a couple of weeks ago and we were dosing my "CJ-QB" with HPA and pushing 14.3's at close to 950 fps at 1000 psi. The QB can handle 1000 psi and quite a number of guys do but it would be much wiser to keep it at 850 or 900 in my opinion. I just don't trust the Chinese...lol... :p ...and you don't need that much anyhow. Velocity dropped to about 825-850 if I recall correctly and that's plenty for me.
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Where can I get a regulater, bottle and one of those coiled lines for HPA?
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Oh and just so you guys know... I wasnt going for a fps title or anyhting. Just thought id try it out so incase someone asked the question... well I wonder how much that mods helps? Then there is a thread for it :)
But keep the good stuff coming !!
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Roy
If you follow this link
http://65.29.172.249:810/Server_Files/GTA/PCP_Conversion_pdf.pdf
It will take you to a file Jason is hosting for me. It tells everything I know about the PCP conversion we used to sell and I have on one of our QBs.
We are working on a different style now, slimmer, easier to fit etc but safety is a prime consideration so development is slow but painstaking.
Bob is right about the consumption. at over 1000 fps a 50 shot between fills QB turns into a 5 shot between fills rifle.
Also it is VERY loud ! We can use noise reducing LDCs here and it's still loud, louder than a CO2 qb at 12 fpe IMHO. Must be the gas speed. He also right about temperature, he posted a very useful temp/pressure chart a while back in the library.
Having a good idea of what MM does to his high power valves and the porting sizes he uses I would have expected a little more, but again, I may be mentally confusing 170 BAR PCP stats with CO2. (Cant find my comparison data at the moment) :(
Also remember the UK law does not allow me to go to these power levels, they were only achieved by accident and the faults rectified immediately, so my knowledge is not the deepest over 12 fpe.
If you want the "full race" tune try a longer valve stem but as has been said, the white clouds are all but wasted gas.
Ian