M4 problematically low FPS

[Freespace535]

I seem to be having some compression problems with my Dboys M4. I tried a Poor mans chrono test this weekend to test it for a game, only to find that it didn't even pierce one side of the coke can - only a very small dent.

I messed with it today, and tested out the piston and all that by covering the nozzle with one finger and pushing the piston into the cylinder to test the resistance. Sometimes it would go very easily, other times it wouldn't. Sometimes the part near the nozzle that has the O-ring on it would slip out. I taped that up a little bit to try and keep the compression.

Then I reexamined my hopup, and got it all assembled about as well as I ever have. I should mention that the frontmost part of the hopup is broken off but held in place. Its the part to the left of the 'u' shaped clamp on the right in this picture

Anyway, even after I messed with those two things it still couldn't put a hole in a coke can with .20g BB's. What else can I do to fix the compression? I am pretty sure thats the problem.

[Deleteplz]

Replace the O-ring on the piston head, it's O-ring number 14 if my memory serves me right.

Also make sure there is a nice coating of lubricant inside the cylinder. If there isn't enough the O-ring tends to dry out.

[Freespace535]

By number 14 do you mean thats the size? So I could just get a replacement of that size?

[Deleteplz]

Yeah. #14 is the size. I have a box of them sitting here.

[Cap n pickles]

If that doesn't work, Check your Air nozzle for cracks, check the Cylinder Head to make sure its not broke (Brass tube should be stiff).

I replace the O rings in all my AEG's i own. it will make a Perfect Seal in the Cylinder. Its great.

[Freespace535]

So even if the O-rings are still intact and the same size and stuff it will make a better seal if I replace them?

Still worth a shot so I'll see what I can do today.

Thanks

[Freespace535]

Well I couldn't find the right O-ring, the place was just a giant wall of tiny cubbies of o-rings lol. Anyway, I did tape the inside of the groove that holds the O-ring on the cylinder head, so its a bit tighter and I think the O-ring on the piston head is actually okay.

I tried the PMC test again was getting around 300 FPS - going through one side but staying in the can. I think air might be escaping in between the brass and plastic nozzles that go out the front of the gearbox - is this a common place for air to escape? I know I can't glue it because the plastic nozzle and tappet plate have to be able to move back and forth. Should this area be airtight though?

[Black Fox]

Check this link out. It provides more detailed information.

http://www.airsoftpacific.com/viewtopic.php?t=30907

[SLINKEY]

you can also strech out the original oring a little bit, its not going to be as good as a new oring, but it will increase the fps if thats the problem. if it does, go get a new o ring, take urs in there and ask the dude that wanders around in that department. he will find it for you.

you can also take some thick lube, with a high viscosity, and put that on the tube coming out of the cilinder head, then take ur air nozzle and spin it on there like a screw, to get the grease all even in there, Id recomend a metal air nozzel with oring, or even a plastic one with oring. there cheap.
And no there shouldn't be any air escapeing between the air nozzle and cilinder head tube thing..
then, check the pistons compression, it should be very hard to push in every single time you push it in. try it with the air nozzle half way pulled off the tube with ur finger on the end of it.

you can also wrap a single layer of teflon tape around the cilinder head, and then it might get a better seal there too, like said before make sure ur cilinder has a nice layer of grease in it, and do all of these in steps, so then when you get a bump up in fps after doing one of these, you know what you need to replace.

if you get them all nice and air tight and ur still only breaking one side of the can, go get a modify 110 spring. Ull be right at 400 again.