A&K M249 upgrade issues (systema parts)

[j_f_oko]

The install went off without a hitch...this mechbox is a dream to work on. I installed the following:

Systema duracon bearing piston head
Systema bearing spring guide
Systema advanced polycarb piston
Guarder enhanced polycarb tappet plate
Deepfire cylinder
Deepfire nozzle
Hurricane Aero advanced cylinder head (didnt fit have to order something else)

With the exception of the cylinder head all parts have exactly the same dimensions.

However after i got everything put back together and tried to test fire i got a half cycle out of it and the piston was stuck at the back of the cylinder and the fuse disintegrated, i had remembered reading some threads about such problems on here before so i checked for some remedies and came up dry. After installing a new fuse, i tried a few more tricks and different batteries but still the same result. I disassembled and reassembled the mechbox at least 5-6 times, checking and rechecking things and swapping parts in and out between the new and old and this is what i found.

With the bearing piston head you're losing some spring space because of the bearing assembly, which is also true for the bearings on the spring guide, so when used together there may not be enough space for full spring compression. Since i wanted the new piston and piston head more than the spring guide i tried just using the new piston assembly and the old spring guide so i would only be losing spring space from one end. No go. But if I use the old piston and the bearing spring guide it works fine, but they both take up the same amount of extra space...still trying to figure that one out. The only thing i can think of is that it has to do with the piston itself because it is a really tight fit sliding the spring into the new polycarb piston and requires some finesse to get it all the way in, whereas its fairly loose when using the old one, maybe the tight fit is hindering the springs compression enough that its stalling the mechbox.

Now, with all of that out of the way i left it as is and just set the new piston assembly aside for now and am happy that my gun works with the few upgrades i was able to get working. Most of the info i've provided is here so that if anyone has any additional insight into my issues they can please let me know. But my main question is this:

Are there springs that differ that much in length that i will be able to fit both the piston assembly and spring guide without any issues? Remeber to keep in mind that the diameter of the spring as well as the length may be contributing to the issue. I have done some searching and from what i've found it sounds like a systema spring should work with these mostly systema parts that i've installed (makes sense since they're all designed to systema's specifications) or so the manufacturer would have you believe. Can anybody verify?

I want to have very similar performance to what i have now, the stock spring is fairly hot which i like, but i dont want to sacrifice longevity of mechbox parts for the sake of fps (anymore than it already is). I would like to keep it at around 365-385 fps. So short version... any spring recommendations for a slightly shortened and narrowed spring chamber that will provide my desired velocity?

I know there are tons of springs out there but not having hands on experience with them makes it difficult to know if they'll fit.

Hope the info i've provided is sufficient, because its a long post. And i'm looking foreward to getting some feedback.

Thanks.

[DENZILDON]

Just found your thread. Here's a thread on filairsoft regarding a&km249.
http://www.filairsoft.com/forum/show...t=m249&page=11

I think you might need a half tooth piston. But from what I have read the A&k m249 should be able to take m130 spring with everything stock. Maybe just a batt upgrade.

Let me know if you need translation in some parts in the forums.

[j_f_oko]

Thanks for the reply...i was starting to think i'd never hear anything.

As for the half tooth piston idea, the stock one was full-tooth so an aftermarket full-tooth should also work. I also tried swapping in a fairly hefty 9.6v nunchuck battery (as opposed to the stock 8.4v) to see if it would move the gearbox but it still would just bind up at the back of piston stroke. I ended up taking the new piston assembly out, made sure it was back in working condition, then threw the gun in the closet and havent looked at it since. But im fairly sure that it had something to do with that fancy new piston that systema has made (http://www.redwolfairsoft.com/redwol...?prodID=23686), the internal chamber of the piston is a very tight fit for the spring and from what i can tell its so tight that it isnt allowing the spring to coil itself upon compression therefore the length of spring inside the piston is binding instead of compressing and stopping the gearbox from cycling. I was going to try a new piston but was tired of waiting on parts, and tired of taking the damn thing apart over and over, so the gun got tossed aside and nothing was ever done to address the problem. I havent come across anybody else with this problem (although i have not been keeping up with the forums since then) which reinforces my theory that its the new pistons fault, just an unlucky choice of parts i think.

Thanks again though.

[DENZILDON]

No worries! How about putting back the stock piston while waiting for a replacement? That would surely test the theory. Either that it can also be shimming?

Right now in my A&K m249 I have everything in stock except for the spring. I've placed an m120 spring in it and currently just waiting for this weekend to shoot it out. I don't know how the stock battery is going to hold though, i think its going to scoop it dry in half a day.

By the way, I tried an SP110 on it and it should shoot around the 365fps mark.

On a side note, I opened up the hop up last weekend and as per arnie's review, the hopup does suck. I wasn't able to copy what he did with that plactic thingy but i managed to replace the hop up with a gauge 16 wire. And it works!!!

[BIGMEDCIN]

My son and I both have the A&K M249 (PARA and MIMIME)

I put new hop rubbers in both and both have a Mad bull M120 spring and thats all, with an 8.4 they still fire at a good rate but my son uses a 9.6 and I use a 10.8.

FPS are close but his is about 15FPS better (better seal?)

we pound on these gearboxes, my son has used his more shooting some 12,000-14,000 or more rounds, I have used my 3 times shooting about 7,0000 round, so far the stock parts are surprisingly holding up!!

The accuracy and range from these are very impressive, his at 395fps mine at 380fps.

[DENZILDON]

Originally Posted by BIGMEDCIN

My son and I both have the A&K M249 (PARA and MIMIME)

I put new hop rubbers in both and both have a Mad bull M120 spring and thats all, with an 8.4 they still fire at a good rate but my son uses a 9.6 and I use a 10.8.

FPS are close but his is about 15FPS better (better seal?)

we pound on these gearboxes, my son has used his more shooting some 12,000-14,000 or more rounds, I have used my 3 times shooting about 7,0000 round, so far the stock parts are surprisingly holding up!!

The accuracy and range from these are very impressive, his at 395fps mine at 380fps.

Awesome isn't it!!! Yeah it might be seal. I did the glass sealant thingy on my hopup. You can try to do that and see if it improves the seal. The instructions should be somewhere in the forums (I got lazy lol).

Are you using the stock batt that came with it? Does it hold up for a day with the stronger spring?

[BIGMEDCIN]

Originally Posted by DENZILDON

Awesome isn't it!!! Yeah it might be seal. I did the glass sealant thingy on my hopup. You can try to do that and see if it improves the seal. The instructions should be somewhere in the forums (I got lazy lol).

Are you using the stock batt that came with it? Does it hold up for a day with the stronger spring?

I think I will just leave it, shoots consistent and straight so if it aynt broke: and I can live with 15fps less. (I am thinking nozzle to hop rubber as is where most clones leak that I have worked on)

no the stock batts were not too bad but typical clone batteries I wont trust them, I use a 10.8x1500 mini from onlybatterypacks.com and my son is using a 9.6x 3200 attached to the para stock.

[DENZILDON]

10.8!!! Wow!! It did not fry anything? even the fuse?

[BIGMEDCIN]

Originally Posted by DENZILDON

10.8!!! Wow!! It did not fry anything? even the fuse?

well the fuse is no longer, but ya I was surprised the fishing line size wiring has lasted?? and it has not been for lack of trying to fry it, some of my bursts have been very very long, I remember going through the entire box in a little under ten minutes while set up in a defend!
so far the M-249s have done very well, we often talk about ok, when they blow up we are going to buy this and that! but they just keep going. like any airsoft they will break but for the money it has got to be one of the best buy for the money airsoft I have done, fingers crossed!

[DENZILDON]

Nice!!! Well, thanks for your replies bro!!!