m4 issues

[hadur]

okay ill start by listing the parts present

http://www.airsoftparts.ca/store2/in...roducts_id=185 g&p m120 gearbox
http://www.airsoftparts.ca/store2/in...roducts_id=771 modify air seal nozzle
http://www.airsoftparts.ca/store2/in...oducts_id=1059 modify ported cylinder


now for the problem. this gun was built from scratch essentially, so the chances of it just working are like.. nil. When i shoot, the bb's fly MAYBE 20 feet and drop like rocks, when i chrono'd it i was running around 250 fps on .28's . I have been told it was probably a compression issue, but im wondering what everyone elses opinion is on it. ( ive also removed the hop up from the question, as i have changed it out for 3 that used to work. )

[andrew5826]

try switching to the original air nozzle. i heard that modify ones dont reach all the way to the hop up so maybe your losing air there

[HKGhost]

Maybe an air seal problem. Remove mag, turn gun upside down, drop in 2-3 bbs in the hop up chamber and fire in semi. If a bb jumps or pop out of the hop up chamber, then you're nozzle is not making a seal in the hop up chamber. 1) sand down the front of the tappet plate so the nozzle moves more forward (there's a guide somewhere on here) 2) replace nozzle with a longer one (the proper one) 3) seek a gun doc or someone with internal experience. Good luck

[hadur]

Originally Posted by HKGhost

Maybe an air seal problem. Remove mag, turn gun upside down, drop in 2-3 bbs in the hop up chamber and fire in semi. If a bb jumps or pop out of the hop up chamber, then you're nozzle is not making a seal in the hop up chamber. 1) sand down the front of the tappet plate so the nozzle moves more forward (there's a guide somewhere on here) 2) replace nozzle with a longer one (the proper one) 3) seek a gun doc or someone with internal experience. Good luck

Would this problem also result in the occasional feeding issue?

[Jackarutu]

"( ive also removed the hop up from the question, as i have changed it out for 3 that used to work. )"

I think we need to hear more about what hopup unit you are using and what lower reciever it is being used in. Sometimes on second look one will find the hopup rubber is not fitting in the hopup unit correctly (might be oval shaped instead of round. . .Etc) If the hopup unit doesn't fit tight up against the gearbox or has an angle to the aligment airleaks will happen.

One common problem is the clip that secures the inner barrel to the hopup unit being to thick and causing the hopup unit to not slide free in the outer barrel base causing it to set to far forward from the gearbox thus causing an airleak.

There can be a mulitude of problems with hopup fitment and function.

[hadur]

I have 2 g&p hop ups, and am currently using a madbull ultimate hop-up(apparently I don't have 3 that used to work.. My bad ) . I did notice that the hop up sleeve was nearly impossable to get all the way in, and the clip is kind of hindering the movement of the hop up unit itself. I debated filing down the clip last night to get a better fit, and I've never liked how the sleeve fit, however I just sorta assumed that madbull wouldn't have included a sleeve that didn't fit .

[venture]

Couple of things are possible here:

1st. Make sure that the little spring on the front of the hop-up unit is present. very important!

2nd. An M4 airseal nozzle should be in the neighborhood of 21.6mm ± 1mm. Longer than 21.6 can show up as misfeeds when firing in full auto. Shorter than 21.6 can begin to show up as double feeds and/or loss of fps due to loss of air seal.

3rd. Ensure hop up is in good condition and not impeding the bb. You have already indicated that you have eliminated this one.

4th. If all these fail to help, then you should open up the mechbox and check for problems there. Could be airseal of piston head, cylinder head, and/or nozzle/cylinder head.

That should just about cover it.

[Jackarutu]

Crunchy,

The madbull hopup at first glance seems like a godsend to solve the problem of the addjustment changing when firing the weapon. However, that said the realities of it are much more troublesome then the problem it solves. In short the answer is cut the rubber length so you can get the clip on. However, the Madbull clip is very thick and sticks up and causes the hopup to get stuck in the outer barrel (instead of sliding back and forth easy). Also you may have to change the rubber that comes with the madbull for one that is easyer to get to fit at the front of the hopup so it is round and not oval where the BB enters.

On another link here there is much debate about cutting the rubber to get the clip on. The endorsement for cutting the rubber comes straight from the US distrubutor for madbull products!

What we need to help solve this problem is one of our machinest friends to take a good look at the madbull hopup using go and no go gauges and also to check if the hole is the same diameter all the way down the length of it. And also if it is at an perfect right angle to the nozzle alingment.

Once you get one to fit and work they do the job quite well.

[hadur]

okay, so i got home and test fired the gun, now its no longer a nozzle issue.. the gun doesnt even cycle, i pull the trigger, and it makes an odd click noise and goes no further... when this is done, my lipo and the wiring heats up immensly.