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Post by luke213 on Mar 13, 2004 12:33:29 GMT -5
Well I've upgraded my M15A4 acctually I did it a while ago like a couple weeks. Now when I did this I fubar'd my cylinder head. So I ordered in a new cylinder head assuming it was the cause for my low chrono results when I checked it. It was running around 315fps for a Prometheus M120, which I am assuming should run in the 400fps zone with a Systema M120. So back on track I replaced the cylinder head with a Prometheus Version 2 cylinder head which is a really nicely made peice by the way. Now I assumed once again it would chrono right around 400 and to my dismay today I just chrono'd it with no hopup and hit a whopping 315fps:(
I pretty well did nothing to the gearbox that should have caused this as best I can tell. This was my first run at upgrading a gun, though I've read through the airsoftplayers guide etc, several hundred times over the last year:) Anyhow any suggestions? Not to mention does anyone happen to know if the Prometheus springs are set on any other kind of scale. I'm planning on asking around ASP as soon as I get back to my house to see what I can dig up, though I figured I would see what anyone else could think of to try. Aside from that the upgrade was pretty uneventfull and I'm really not sure what else would cause this drop in FPS, since I'm pretty certain I've lubed the right area's etc, everything in cycling normally, and I've got it timed correctly. Either way I'm bringing the chrono with me to be able to test it this week while I piss around with it at home.
Any suggestions are more than welcome as this seems to have me stumped.
Thanks
Luke
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Post by DE50man on Mar 13, 2004 16:08:38 GMT -5
Might your nozzle be broken? That would be the only thing that seems would cause that low fps, unless it was on a different scale to systema
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Post by luke213 on Mar 13, 2004 16:15:40 GMT -5
Well it's a brass nozzle(or brass colored definatly not plastic like TM) so I would say thats a no go, and the cylinder head seems to fit nicely not to mention on an initial compression test prior to putting it back together it wasn't leaking at all.
Also this spring was considerably longer than my stock spring roughly 2in, perhaps a little less though a real pain in the ass to install. Now my initial spring was pulling down nearly the same FPS though smaller which leads me to believe that it should be shooting 400 also. Though with their progressive coil or whatever who the hell knows. I'm more frusterated than anything at this point. I may have to set this project aside for a little bit till I get some money to try replacing some things, though really at this point I'm not sure what to replace.
First impressions considering the other things I would think maybe the o-ring on my piston head got fubar'd somehow, though after checking compression I don't think so. Hell I just don't know at this point.
Luke
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Post by Knief on Mar 13, 2004 16:28:04 GMT -5
Could it be that the cylinder got flipped around? Some cylinders have a hole in them to reduce the compression volume to match barrel length (so something like a carbine is likely to have the hole). If the is supposed to be near the back, but you flipped it so it's at the front, you'll lose a lot of volume. It happened to me on a G36.
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Post by luke213 on Mar 13, 2004 16:33:51 GMT -5
Shit you might be onto something, I know I put the hole on the other side, though damnnit I could have flipped it and not noticed. GOOD CALL! Luke EDIT: Wasn't that.
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Post by luke213 on Mar 13, 2004 16:51:32 GMT -5
Just checked and unfortunatly it's not the cylinder hole as it's facing the rear of the gearbox.
Luke
EDIT: It appears redwolf says the springs are on another scale, though still hiting lighter than it should, they claim around 360-370, which on a high shot is only 30 or so less. Either way I think I'll just pick up a PDI spring and say piss on it.
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Post by Munin on Mar 14, 2004 21:11:42 GMT -5
Make sure that you lube the crap out of your piston head with heavy silicon grease. This keeps any kind of leaking around the piston head (which robs you of pressure, and hence FPS).
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Post by luke213 on Mar 16, 2004 18:51:46 GMT -5
I took it down again tonight, damn the 2AM mechbox repairs Get bored and decide to piss around with it. Anyways I tested compression again as I was doing things just to see where I'm loosing some(I assume somewhere) since I'm still 50fps or so short. Anyways I relubed the piston head and cylinder head, not to mention the part of the cylinder head which goes into the nozzle. Reassembled, as I did I noticed a few things(well before I tossed the box back together), that when putting my finger over the end of the nozzle and doing a compression test I had quite a bit of resistence. Then I took the barrel assembly with hopup attached and tested compression all the way to the end of the barrel. I seemed to be loosing quite a bit in the hopup chamber.
Here's the question, does the hopup bucking actually seat and make the connection with the nozzle? I would assume it's what works as a seal between the barrel and nozzle.
So I disassembled my hopup chamber, pulled the barrel etc. Made sure everything was lined up and the bucking was all the way back on the barrel, then reassembled and I seemed to get more compression. So if it does make the seal perhaps I had something wrong there. I can't chrono it tonight as I don't have enough light to get it to chrono and my brother is sleeping and he can't hold the chrono closer to the light source etc, and I don't have enough hands to do it all myself
One additional thing I noticed while reassembling, is that I beleive my wires could have been getting in the way of the hopup chamber coming into full contact with the nozzle which also could have been a problem, so hopefully after re-routing the wires thats no longer an issue.
Overall if someone knows for sure about the hopup question I'd be interested and I will post results of a chrono probably first thing in the morning, though thanks for all the suggestions in this. Really just couldn't figure out what the hell was going on, it's one of those situations thats hard to see what the hell is causing it. Though as I said I appreciate the help.
Luke
EDIT: One additional thing, if I hadn't mentioned it before that m120 is supposed to push 360-370 not 400, so just a warning to anyone buying Prometheus springs as they are not on the same scale as Systema or other brands.
EDIT2: Chrono'd it this morning and saw righ in the ballpark of 360-370, really unstable chrono(didn't have a table etc with enough lighting) so I'm gonna assume it's right around there, tomorrow I'll get to chrono it outside then I will know right where it's shooting. Anyways if anyone knows the hopup question post.
Thanks
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Post by Bigmack on Mar 16, 2004 19:34:42 GMT -5
Are you saying that the prometheous M120 is weaker than the systema one?
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Post by luke213 on Mar 16, 2004 19:52:24 GMT -5
That I am:)
According to redwolf, which is the only place that lists an FPS for the springs they are rated for 360-370 rather than the usual 400. Which is really a pisser because I didn't realise it when I bought it, and now intend to finish this upgrade with a PDI spring and a few more upgrades to hit the FPS mark I was going for in the first place. Though this spring will likely just go in one of my other long guns and call it good. Either way though yes the Prometheus springs are on some other scale and someone on ASP had mentioned it though for the life of me I can't find that post now.
Luke
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Post by Arc on Mar 16, 2004 20:13:10 GMT -5
How does that work? I thought that the "M" rating referred to the spring's expansion rate in meters per second (90m/s being stock). Is Prometheus just abusing the system for sales reasons, or is there a better reason for this?
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Post by luke213 on Mar 16, 2004 20:19:20 GMT -5
My assumption is that considering it's a new line of products that perhaps that retailers just aren't listing them correctly. I can't find the packaging from the spring at the moment though I believe it was listed as a SP120 or something like that though most of the places selling them list them as an M120. So I would think that it's all a misunderstanding as far as the way they are being sold. I also think it will get straightened out though it's just gonna take some time.
Luke
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Post by Knief on Mar 16, 2004 20:19:47 GMT -5
if "MXXX" is the springs expansion rate, then it would be a safe bet that prometheus springs are shorter than systema springs. Basic physics, Elastic (spring) work= (1/2) (spring constant, i.e. MXXX) (displacement)
So if a spring has the same spring constant (K), and puts out less work, physics would say that it's a shorter spring.
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Post by luke213 on Mar 16, 2004 20:23:44 GMT -5
Well not necisarily as I believe PDI springs are *shorter* though the spring tension is also related to build material and diameter of the wire used for the coils.
Luke
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Post by Bigmack on Mar 16, 2004 20:30:54 GMT -5
using Systema as an example...their springs all seem to be the same length.
Just going by pictures...compare the M120 and the M160 at WGC. the wire on the M160 is noticeably thicker.
I'd suspect that a different metal would be used to get a more dramatic effect.
stronger steel = stronger spring.
Course, i'm just guessing at this...but it seems logical to me.
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