M4 FPS Problems

[Spudbum]

Hi Guys

My brother and I have the same guns. JG M4 S-System

Mine used to fire at 349.8 FPS
My Brothers around 320 FPS

Right, well, my piston head and piston sheared so I bought new ones from my local airsoft shop.
I also fitted them.

After, I attended a game day and i was only chrono'ing and 250. Pretty embarrassing.

I therefore took the gearbox apart and checked my compression. Pretty good. However there was a small leak. Put PTFE tape around the cyclinder head. Job Done

I still seem to be getting significantly lower power than my brothers and would like it back up to 350, considering the money i have spent.

I am on the verge of taking it to the shop and telling them to get on with it, but dont know how much they'll charge me

I have attached a video if its any help

http://www.youtube.com/watch?v=xp9p5qFmCpo

Any ideas will be greatly appreciated

Cheers

Dom

[Gaffa]

Re: M4 FPS Problems

If you've not changed the spring, and it was left decompressed (Semi Auto shots at the end of the day), then you're still going to have an airleak.

The most common form of airleak is either, the piston moves into the cylinder when your finger is over the nozzle (piston should want to bounce straight out), or between the nozzle and hop unit, then hop rubber.

[North West Outpost]

Re: M4 FPS Problems

This may help, especially the cylinder component bit.

http://www.zeroin.co.uk/showthread.php?t=104456

[Spudbum]

Re: M4 FPS Problems

Ok cheers.

I looked at that link and will try that tissue paper leak test tomorrow
I'll let you know how I get on.

Just to note, I have only just recently put a new madbull rubber in and a new hopup

[HuntR]

Re: M4 FPS Problems

Was it a madbull hopup by any chance. If it was, make sure you A. Leave off the little o-ring at the bottom of the unit. B. Make sure you didn't use the nub that came with the unit.

The nub causes fps issues as it's too darn big. Also causes jams and misfeeds.

The little o-ring on the bottom of the unit causes jams and misfeeds but not fps issues.

If you have left out the o-ring and replaced the nub, then i'd recommend checking the seating against the gearbox casing. My hop unit is very tight in my upper and doesn't spring back against my gearbox. To combat this easily don't put the hop unit all the way in the upper receiver. And use the lower to push it forward just far enough. If you don't get what i mean i'm sure i could make a quick vid for you.

[North West Outpost]

Re: M4 FPS Problems

I had a similar problem in a G and P.

I wasnt quite sure what he meant by the tissue paper thing...lol.

So long as your gear box is functioning properly, yes as Hunter says.

If you put a madbull buffer next to a normal one they are huge. It is easy to see why they cause problems.

Some thin rubber strip can be invaluable, in fact the bit I was going to send to Hunter, I found in my pocket today...oops!

[HuntR]

Re: M4 FPS Problems

Indeed Midas. You can hold on to it for me until my gearbox comes back to you for more work.

If you've installed a non Ultimate unit, then i think it's most likely your cylinder head and air nozzle. I had a dboys M4 that did exactly what yours has done. I put a Guarder cylinder head and air nozzle in there and it fixed it right away.

[Spudbum]

Re: M4 FPS Problems

I have the standard 2 piece hop with the blue madbull rubber.

I have tried that tissue test, no airleak from the bb feed.
I have pulled the barrel and hop out and used the gearbox to push it in. Ensuring a tight seal. Still no improvement.

The fuse does seem to get a bit warm when firing.

Any ideas?