M249 Piston advice needed they keep breaking :-(

[beagle182]

Hi All,

So i have a A&K M249 - and i go through a piston every 10 min - no joke it blows a piston in about 10 min of game play ROF is mental on 7.4 lipo I was wondering if there is a piston that can handle some serious abuse.
I dont REALLY want to slow it down as it is an awesome bit of kit for like 10 -20min and then teeth tear off the piston (and just FYI this is not me holding the trigger down its controlled bursts) and thats clean off with the metal ones i.e. teeth out of the body of the piston.

As far as i am aware everything else within the gun is perfectly fine - i have had it looked at by professional in store mechanics (shall not name) and same thing happened.
Even they said ROF is awesome for support weapon.


I have tried the following pistons in it:

MADBULL Alien green polymer Piston w/ MIM processed Metal Teeth (FullTeeth)
Deepfire Piston with full teeth for AEG
MADBULL XF Piston (Full Teeth)
+ about 3 more i cannot remember

If anyone knows of any piston that lasts better than another on high rate of fire PLEASE let me know

Thanks

[Caldymoose]

Re: M249 Piston advice needed they keep breaking :-(

well if it keeps blowing pistons, then there is something not right with the gun.

From what you've said with your 'mental' ROF, what actual is it? And what spring are you using? Has the AoE been corrected and a sorb pad installed? Has the 2nd to last tooth on these previous pistons been removed? Has the gun been short stroked?

It sounds like your getting pre engagement, most likely caused by running too weak a spring. but without specific details it hard to say.

As for a replacement piston, Lonex Red. Tech in Scotland who does a lot of high end, one off builds uses them all the time in his builds. If it can stand up to a DSG running an 11.1v LiPo big enough to jump start an aircraft carrier then its fine for a build. Provided the rest of the gearbox is tuned accordingly

[TS_Welshy]

Re: M249 Piston advice needed they keep breaking :-(

As above - the piston isn't the problem. If they are going that quickly you clearly have a major gearbox issue, and it is most likely pre-engagement.

This is where the sector gear begins its second cycle before the piston has returned to its starting point. As a result, the sector tooth and the first tooth of the piston smash into each other from opposite directions, which clearly exerts a lot more stress on the piston teeth. They also won't engage at an ideal angle, meaning bits of the piston can get chipped off, and eventually break.

You can reduce the chance of this happening by fitting a stronger spring and reducing weight of the piston, which allow it to accelerate more quickly back to its starting point, ready for the sector gear.

You could also have an angle of engagement (AoE) problem: quite simply, even at the rest point the sector gear and piston tooth are not engaging at an ideal angle i.e. the faces of each are not flush (which maximises the spread of forces and minimises pressure), so you get edges hitting each other (smaller spread of force and more pressure) creating more wear. You can see this effect with 'Helical' gears which have sloped teeth to maximise the contact patch between each other.

Some points of advice I would give for the future:

1) (and if I could type this in font size 72 I would!!!) DO NOT USE METAL TOOTHED OR FULL METAL PISTONS!!!!! EVER! EVER! EVER! The piston is a mechanical fuse, and if you have a poorly set up gearbox (as you do...) it is far better for a £20 piston to get shagged to let you know there's a problem, rather than a metal piston AND a £50 gearset tearing each other apart.

2) Don't put so much faith in airsoft retailers repairing your gun. They have one priority in this situation - maximum price for minimum input. Find a friend or user on here who is very competent with airsoft guns, and will take the time and care to put your gun together and shim the gears properly and carefully to get it working well.

3) Why do you need such a high rate of fire? It causes so many problems for very little benefit:

- As you have already seen, the chances of a high rate of fire gearbox eating itself are much higher than normal. You also need lighter and stronger parts which are more expensive (plus better motors, lipos, wiring, MOSFETs etc).

- It wastes ammo and there are no scenarios in airsoft where you actually need particularly high rates of fire. Repeated, accurate bursts of 3 or 4 rounds will keep heads down just as effectively as a burst of 35 rounds will. (Even one well placed round that pings loudly off of hard cover is usually sufficient!)

- More chance to simply inflict pain on other players, which is really not cricket. 3 or 4 rounds as per the description above hurts.. 35 REALLY f'ing hurts, and for no reason - you only need to be hit once to be hit, but 3 or 4 reduces the chance of you missing, clearly. If you NEED to spray 35 rounds in a second to hit somebody, then you need to look at your hop rubber (or lack of) and check your weapon's accuracy.