Dboys m4 shooting issue

[Payback]

So today was the first day for me to use a new used m4 i got. The issue i'm having is the gun will shoot about 4 rounds, shoot 1 round nothing, then 3 or 4 rounds, then 1 or 2 nothing.

I first thought the mag wasn't feeding properly, but i used highcaps, 2 different typed of mids, all work fine in my other gun, but in the m4 it just doesn't feed right.

When it misfeeds it does cycle and shoot air, just no bb, i do think every now and again it doubles a bb out.

Question is, where do i start looking? Could it be the hopup? something loose? Gun is basically stock other than a tbb.

Thanks for the help.

[Jester316]

Turn the hop up all the way off. The whole hop up unit might be mis-assembled. The loading nozzle may be broken. The tappet plate may be broken. These are listed in easiest to hardest to diagnose.

Also, check to make sure the little spring on top of the hop up unit is present... just for shits and giggles.

[Payback]

Thanks, I'll start there, I had a feeling it would be in that area but wasn't positive.

[pseudoanimosity]

Also, try to make sure your outer barrel is in straight, this could throw off the hop up, and make it harder for the hop up to engage the magazine. The easiest way to do this is to take out the mag, and just make sure the seam on your hop up lines up with the seam on your gearbox.

[Payback]

Could it be an issue with just the bucking? When I pulled the barrel out the bucking stayed inside the hopup. I changed to the shorter barrel, and still had the same mis-fire problem.

[Jester316]

I'd replace the bucking.

Also, you refit the bucking on the new barrel BEFORE you instered it into the hop up chamber, right?

[Payback]

I'd replace the bucking.

Also, you refit the bucking on the new barrel BEFORE you instered it into the hop up chamber, right?

Umm, yes now I did,

[Payback]

So i got a madbull hop-up today, blue bucking. Got it all put together with some finessing. Put the barrel hop-up in the gun, shoot it, and........nothing. Actually it put 1 bb out.

So i go looking at if its feeding properly, put two different types of mags in it, still nothing. I take the outer barrel off, put just the barrel and hop-up on the nozzle and see whats not lining up, i can't see anything, but still wont feed.

Then i drop one bb in the hop-up, shoot it and it fires fine.

I got looking at it, and the nozzle isn't moving back and fourth any more like it had. Could this be a broken tappet plate? or a broken nozzle? The air pressure coming out of the nozzle by itself is ok, but when i put it all together its nearly nothing.

Any other ideas? places to look? The hop-up and bucking is all lined up really good, so i doubt i installed it wrong. I've quadruple checked it.

[MillerSA15]

So i got a madbull hop-up today, blue bucking. Got it all put together with some finessing. Put the barrel hop-up in the gun, shoot it, and........nothing. Actually it put 1 bb out.

So i go looking at if its feeding properly, put two different types of mags in it, still nothing. I take the outer barrel off, put just the barrel and hop-up on the nozzle and see whats not lining up, i can't see anything, but still wont feed.

Then i drop one bb in the hop-up, shoot it and it fires fine.

I got looking at it, and the nozzle isn't moving back and fourth any more like it had. Could this be a broken tappet plate? or a broken nozzle? The air pressure coming out of the nozzle by itself is ok, but when i put it all together its nearly nothing.

Any other ideas? places to look? The hop-up and bucking is all lined up really good, so i doubt i installed it wrong. I've quadruple checked it.

The tappet plate is almost definitely broken if the nozzle doesn't move. if you nozzle broke, you will be able to just pull the nozzle off the end. The only other possible cause would be the little metal tab on the gear that pulls the tappet plate back broke, but I have never heard of that before.

[Payback]

Well, i was hesitant to open it up since i have never done so before (have watched countless videos on how to), so i opened it Yes the tappet plate is broke. The teeth on the piston are also chewed up.

So i'm looking at a new tappet plate, piston, might as well do the cylinder if they arent too expensive, a new nozzle, and also i'm going to replace the nylon bushings with bearing bushings, and try to add some more shims since it was really bad the way it is now.

At least i know if i screw it up, the great guys at aonw can bail me out, just hope i can afford it.

grrrr, used guns, buyer beware.

Any suggestions on the parts i listed? I have about zero idea right now on what is good or bad for internals, i had never planned on doing it this soon after purchase. I also don't want it to be too fancy, since it is a dboys, and i want to keep it under the fps rules for our fields.

[Payback]

Got new bushing, piston, tappet plate, and nozzel. The gun shoots, but the bushings stick out of the gearbox too far and makes the selector switch not work. Was told I'm either s.o.l. Or to use a wet stone and sand them down without causing too much heat. Almost thinking about putting 2 nylon bushings back in the problem spots to get the clearance.

[Jester316]

I had the same issue with my dboys. I had Mike (Ash) fix it for me. I can't remember what he did, but he might have just gone with nylons for that one gear...

[Payback]

Well, i used a dremell and honing oil and ground it down ever so slightly. Deburred it and rounded the edges. Fits and runs great now.

Just have to figure out the feeding problem i have now with the madbull hop up. Might just gut it and put the parts in the original hopup.

Also took about 8 times of assembly and dis-assembly to get it working, seemed to have a different issue each time i did it. But works great now. Private game tomorrow to run it and see how it works.

[UnHoly8807]

If the bucking isn't perfectly set then it will miss feed. Im not sure with the dboys but with my kwa this truly is a phony pony.

Also a friends g&g wouldn't feed with mad bull blue and had to go with the red.I never trued to figure out why and his gun is very far from stock.

[Payback]

Last update on this, Gun shot great, perfect hop up adjustment, i got shots out to 150 ft plus.

Just it doesn't feed my p-mag midcaps now. I've torn it down and found that the little spring release deal on the mags is shaped different than on the high caps, so i have to push up on the bottom of the mag to get it to release the spring and feed into the hop up. I'm guessing that the new hop up isn't sitting as low as the other. Not sure how to fix it, but moving on to new things