A&K M249 hopup repair / replacement

[Jackarutu]

The following is what I have observed from studying the M249 Hop up.

The first thing that came to my attention was the fact that the hop up adjustment selector when assembled onto the hop up unit goes on in the half way adjustment position. The inside of the adjustment selector has a cam that goes from zero to full engage as you turn it. Thus when you assemble the selector onto the body the standard nub (as comes with the weapon) fits to the cam @ zero bucking even though the selector is already half way engaged.

What I don’t know is if one were to make a custom nub that was longer than the standard nub would it have a positive effect on accuracy?

If the nub were longer it would mean that to assemble the selector to the body one would have to push the nub into the body and then while holding positive pressure on it slip the selector over it. Thus when assembled one would already have half of the bucking range engaged. However if the nub were cut to the correct length it should go to zero bucking when the selector was turned to the full off position. To answer this question I have made some differing length nubs out of drill stock but to date haven’t had time to test them so I haven't found the ideal length yet. Also remaining is the question of if a metal nub will shorten the life of the bucking rubber sleeve?

Also of interest is that the nub is positioned onto the bucking rubber in a different position on the M249 then other AEGs. Instead of laying horizontally across the inner barrel cut out it is vertical. This means that only the diameter of the nub engages the bucking rubber. This also implies that those fancy nubs such as Xs and Hs would not fit or be of any benefit for the M249.

One last thought is that because there is no key in the main hop up body to engage the barrel it is possible to put the barrel in upside down. If the barrel is installed upside down then no bucking is possible regardless of where you set the selector because the nub will not engage into the barrel in this position.

[Cpl T. Syndrome]

Hey Crunch, an easy fix to raise your ROF is to get a G&P 9.6 3600 mah large type battery and re-wire with deans..

[Trunk]

Originally Posted by DENZILDON

What's up crunchy?!

What I did was I changed the hop-up rubber and I used a piece of 16 gauge wire strip (no wires inside) as a bucking. (very responsive). Trial and error on how long you need to cut the strip.

You can also place a material in between the original bucking and the cap to close the gap and get the bucking to push further. In Arnie's review he used a piece of plastic packaging.

I also did the glass sealant airtight mod. Currently mine is shooting an average of 390 to 400fps with an m120 spring. No other upgrades and stock batt.

Denzildon-
I know this thread has been dead for quite some time, but I was curious to what you meant by the glass sealant airtight mod... can you explain?