HELP, FPS all over the map!!

[Cpl T. Syndrome]

I have a TM M4A1

Upgrades:
reinforced mech box-Deep fire
torque up kit-Guarder
MS120 spring-Prometheus
bearing spring guide-unknown
metal bushings-unknown
motor-stock TM 1000
battery-G&P 9.6 nunchuck

Gun cycles fine and strong on semi and full..Rate of fire is fine and strong..Went to chrony cause I figured I'd have to down size the spring..The thing was shooting anywhere from 143 fps to 285???..tried a couple other aeg's on the chrony to make sure it functioning properly and all seemed ok..Any idea's??? I'm thinkin an airleak but has all new parts..Freakin baffling

[TokyoSeven]

Check the hopup. Make sure everything is cosure there. If the hopup and the barrel are not aliged during fire that may explain the leak for some shots and the low FPS, but theres gotta be more that just that I think.

[Crunchmeister]

Wow. That's a pretty big variance in terms of velocity. With that spring, you should be easily shooting in the high 300s, if not over.

The first thing I would check is that the piston is seated correctly, moving freely and is well lubed. A sticky piston could cause those odd numbers. Next, I'd check the piston / cylinder assembly for air leaks. It's possible that your piston head's o-ring isn't sealing with the cylinder wall tightly enough. Or perhaps the sylinder head seal is allowing air to escape.

Also, check the hopup to make sure it isn't the problem. Actually, check this first, since it does't require disassembly of the mechbox.

Best I can do in terms of suggestions in terms of fps problems I've experiences with my guns.

[namloot]

Originally Posted by Crunchmeister

Wow. That's a pretty big variance in terms of velocity. With that spring, you should be easily shooting in the high 300s, if not over.

The first thing I would check is that the piston is seated correctly, moving freely and is well lubed. A sticky piston could cause those odd numbers. Next, I'd check the piston / cylinder assembly for air leaks. It's possible that your piston head's o-ring isn't sealing with the cylinder wall tightly enough. Or perhaps the sylinder head seal is allowing air to escape.

Also, check the hopup to make sure it isn't the problem. Actually, check this first, since it does't require disassembly of the mechbox.

Best I can do in terms of suggestions in terms of fps problems I've experiences with my guns.

+1
good advise

[TokyoSeven]

Im with Crunch on the piston, it could be binding. Hopefully its just he hopup and it can be fixed without opening the mechbox.
And Um....one time I took apart my mechbox after consuming 7 pints of strong bow and I accidentally put my cylinder in with the port forward. So even though its highly unlikely, you maybe wanna check that too.

[Rock 'N' Roll Outlaw]

Strongbow FTW!

[Crunchmeister]

lol I have to agree with TS there. Not a good idea to be playing inside your guns when you're catching a buzz. Be your poison Bud or bud, it's better to do your tech work when totally sober.

Yeah, I'm still pretty a noob but just sharing the problems I've encountered that have resulted in similar results. Good luck with your gun.

[Rock 'N' Roll Outlaw]

Originally Posted by Crunchmeister

lol I have to agree with TS there. Not a good idea to be playing inside your guns when you're catching a buzz. Be your poison Bud or bud, it's better to do your tech work when totally sober.

Yeah, I'm still pretty a noob but just sharing the problems I've encountered that have resulted in similar results. Good luck with your gun.

I'm sorry, I was under the impression you become anything but sober from beer-flavored water such as Budweiser

[Jar|-|ead]

your spring prometheus ms120 should shoot over 400fps..around 420-430fps.

[CDN_Stalker]

Try lubing and using a small screwdriver shaft to stretch your O-ring on the piston. I've found odd extreme variations such as your's with ported piston heads, namely new ones. Stick the small scredriver under the O-ring, get the shaft under it and pull the ring about 1/2" away from the head, then rotate the screwdriver around the head a half dozen times to make the O-ring stretch out. Could just be that sometimes there is a bit of compression, enough to inflate the O-ring to give higher readings, and other times not enough causing lower readings.

Could also be that the piston is sticking (as above), found that before too, and could be improper sealing between the air nozzle and the hop up rubber.