GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Scubajeeper on February 25, 2015, 01:09:44 AM
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Who has done an hpa conversion on an 850? I've recently finished mine and I'm having some issues, evidence is pointing toward a non functioning reg, I think I'm getting full
Pressure to the valve because it shows symptoms of valve lock when I fill it and when it gets down around 2000 the speed starts to come up. Anyone had this problem?
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A malfunctioning regulator sounds like the right diagnosis based on that symptom.
What regulator is it, and have you modified it?
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It's a Chinese eBay special, I've ordered a new one from JDS, when it gets here I'll swap it out and see what happens. I've made no changes to the reg, but I have no way to check the output either, so I'm not sure sure that it putting out what it's suppose to, there were no labels or markings to indicate what the our put was set to, I was just relying on what was in the eBay discription.
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That should do it. JDS regs are solid by all accounts. Out of curiosity, what pressure will you be running and what caliber is the 850?
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It's in .22 and I'll be running 1800.
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The JDS regs are solid. I have a couple of the chinese ones and the ES and SD get much bigger with them.
Why 1800? I think it is a big high but I don't know enough about the H850s. My disco runs on 1600psi and I can get up to 40fpe out it. That's with 30cc of plenum.
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I agree with Dan, 1800psi is pretty high. I have not worked on the 850 platform but the QB and Disco platforms do well at 1400 - 1600psi if the air passages are pretty free-flowing. I guess you can always choke it off a little at the transfer port if it shoots too hot, but you'll lose a few shots per fill because of the higher reg point (1200psi delta between fill pressure and regulator setpoint).
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Using a short adapter keeps the bottle up against the stock and hides the reg for a clean look, the down side is that there isn't much volume, I was just following the info I got off of the 850 resource index. I'm assuming the extra pressure is needed to make up for lack of volume. What are your thoughts on this?
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Yes, that makes sense. When a small-ish plenum is at play, increasing the reg point will compensate...essentially helps you get similar _average_ pressure throughout the shot cycle as one with a larger plenum.
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Here's one I put together several years ago.
It's a .177 with a Ninja tank & reg. set at 1250 psi. Shoots JSB 8.4's at a very consistent 910 fps. Very accurate. When it was still in the plastic stock, accuracy wasn't all that great. After bullpup conversion, it shoots like a laser. Must be the solid barrel mounting that made the difference. The 850's are a great bargain when set up properly.
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Sharp looking gun, I would really like to put mine in wood, I'm not a fan of synthetic stocks. Steve Corcoran made them for a while but he won't build them anymore, I wish he would, those are some sweet looking stocks.
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Not much out there for the 850's stock wise. I made that one out of poplar and stained it with Minwax "Gunstock" stain. Didn't turn out to bad for a first attempt.
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Well, I put the new reg in and an 850 store hammer spring, the first few shots with JSB 15.89's averaged
890 fps. I shot it a while and I guess what has happened is the hammer spring has settled in. It now shoots a very even 854 fps, never varying more than 2 or 3 fps for around 72 shots. Not real happy with the velocity, but it shoots some crazy groups, 25 yards is basically one hole and 50 is not much bigger than 1/2 inch. I'm thinking I might try putting a piece of lead in the spring hole, this would give me a little more preload and add a little hammer weight.