Very low FPS

[Spike]

I got a new Classic Army m4 X series, and it was shooting anywhere from 300-350 out of the box. The spring that was in it when I got it from revolution was not irregular.

I installed a Guarder 110 spring (irregular end to the spring guide), checked the compression (perfect) and airseal in the hop up (also perfect) and now it shoots an incredibly consistent ~200fps, and after about 10 shots it slowly climbs to 220fps and stays consistent there as well.

I swapped the CA motor the minute I fired it as it sounded like a dying cat. I have an EG1000 in there now and I also tried a Matrix 3000, neither helped.

I also tried several voltages of batteries, still no dice. Any ideas?

[Tankdude]

tappet plate attached to the nozzle?

Is the tappet spring attached correctly?

[CDN_Stalker]

He has BBs flying out, so he must have the tappet in the slot properly, can't put it on the front of the slot (won't fit) and behind the slot the nozzle wouldn't move.

This is one of the od things I found with the inflating O-ring type piston heads, great compression on the bench moving it slowly forward to check, but put in the gun and miserable results, O-ring inflates occasionally and erratically. Could be not enough or twoo much oil on the pistonhead?

Oh ya, if it's the stock yellow CA piston and head, remove immediately and put something at least semi-useful in there.

[Spike]

The thing is though, the FPS is very consistent once it settles, so it doesn't seem like there would be an air leak, especially one causing a 150+fps drop.

I already have parts ready to order to replace most of the gearbox anyway, so hopefully that magically fixes it.

One other thing I've noticed is that the piston won't return to the same spot every time in semi, like it's over cycling, even with a regular motor and 9.6v battery.

[Deathfox]

sounds like its more than one thing.... The inconsistent Fps could be from too much lube in the cylinder or hop-up. Also try using a different hop-up bucking and piston head. Like stalker said, there... well....crap!
Also stretching out the o-ring on the piston head helps, sometimes they come a little small and can leak at high pressures.
Try putting the stock o-ring back, guaranteed you will have an fps increase just by doing that.
200 fps is low for a m100 spring, so i dont think its just one issue

[Spike]

bump, just tried a spring that I knew was supposed to be 340ish (came out of another one of my guns) and same thing... low-mid 200s. Compression is still perfect, I'm running out of ideas :/

[L473ncy]

The only thing I can think of is that the piston is getting hung up on something inside the gearbox.

Maybe there's burrs on the "guide rails" for the piston resulting in friction? However that wouldn't explain that significant of a drop. It has to be a combination of a few things causing lots of friction if when you take out the compression unit and test the airseal is seemingly perfect.

[ozzy5]

did you make sure the ports are not backwards

[dpvu]

How are you checking compression? Try taking everything except the cylinder, piston, tappet and nozzle out of half your mechbox. Pull the cylinder back, hold the nozzle forward and the cylinder in place with one hand. Seal the nozzle with your finger and then try and push the piston forward. It should be very difficult to do. Do it with the piston all the way back, in the middle and near the end.

[Spike]

Originally Posted by ozzy5

did you make sure the ports are not backwards

First thing I checked, it's not that.

Originally Posted by dpvu

How are you checking compression? Try taking everything except the cylinder, piston, tappet and nozzle out of half your mechbox. Pull the cylinder back, hold the nozzle forward and the cylinder in place with one hand. Seal the nozzle with your finger and then try and push the piston forward. It should be very difficult to do. Do it with the piston all the way back, in the middle and near the end.

Air seal in all the compression parts is perfect, the piston won't budge when the nozzle is plugged. I also tried the put BBs in the hop up unit upside down test, no leak there either.


One thing I did notice though is that the piston doesn't always return exactly to the front of the gearbox after every shot in semi. Sometimes it's partially back. Would that have anything to do with it?

[Stealth]

Check that you don't have a leak between the nozzle and hop-up rubber.

Hold the gun upside down and put a small piece of tissue into your feed nozzle of your hop-up unit. Fire your gun a few times in semi. If your tissue moves or gets shot out, then you have an air leak there.


Your piston not returning to the fully forward position has nothing to do with it. It just means your motor is continuing to pull the piston back after electricals are cut-off. It's part of the natural momentum of the piston. The more powerful the motor/battery combo, the more this will happen, so much so that some guns will double-shoot in semi. This has nothing to do with your problem.

Does your gun 'sound' any different from before?

[L473ncy]

Originally Posted by Spike

One thing I did notice though is that the piston doesn't always return exactly to the front of the gearbox after every shot in semi. Sometimes it's partially back. Would that have anything to do with it?

That's related to running too high torque of a motor + high voltage battery with a low rated spring (and high speed gears).

It's quite noticeable if you have a torque motor speed gears and an 11.1V pulling an M90 spring, in fact you might even double or triple feed with that kind of setup.

That problem is easily solved by running a lower torque motor (ie. get a standard motor if you have a torque in there or a speed motor if you have a standard motor). However it's not like that specific setup where the gears overspin and the piston is slightly pulled back is bad for the gun or anything.

[Deathfox]

well. After reading this thread again, i realized its very odd for a aeg to ''climb" up in fps and stay consistent. So im thinking the o-ring needs to be stretched a bit, or there is too much grease in the piston head getting things all gummed up. Either or, it seems like the gun isnt sealing properly under higher pressure (assembled) .
But out of the two. i would say your o ring on the piston head needs a little stretch.

[Rusty Lugnuts]

SO only the spring and motor were changed? You did say that you had parts out checking seals- The answer has to be in the parts that were touched. I say that an o-ring got pinched or maybe the tiny one in the noozle came out. I'm afraid your going to have to start replacing parts one by one untill solved
i have replaced piston heads and lost 30 fps but your talking 100 + fps Thats a lot You did'nt put the cylinder in with the port at the front by accident? How is the rate of fire-unchanged? i guess with changing the motor you can't tell... Does it seem like somethings dragging- i once reassembled mine with the piston not in the grooves and it still worked only kinda dragged.

[lurkingknight]

don't think a missing o-ring from the nozzle could drop the fps that much.. though it depends on how much thenozzle gets pushed around by feeding BBs. I would hedge more on piston head o-ring being messed up.