King Arms M4 Feeding Problems + Ammo Problems
 

I've tried some of the advice from other threads, but so far everything I've tried seems to make the problem worse.

Original Problem: My gun was not feeding, or would feed the first few shots and then would miss until I removed and reinserted the mag. Seemed to be happening on both my King Arms and MAG brand midcaps.

Last week I changed the bucking and nub with a modify flat hop hard type, and added a piece of loop Velcro to the inside of my mag well to stiffen up the mags.

Results were again hit and miss, but now I was having the added problem of double-feeding, or at least now I noticed the double-feeding...

Today I opened up my gear box, cleaned it out and re-shimmed my sector gear a bit tighter (it was loose before). I also changed the stock air nozzle with an aluminum SHS one, and put a new O-ring on the piston head.

The gun cycles fine, the nozzle oscillates and I can feel air leaving the end of my barrel, but now the gun doesn't seem to shoot anything at all?

Edit 2015-10-24: Gun is back to normal after putting back the stock nozzle. The SHS aluminum nozzle was too long, then I filed it too short which created different problems. See my chart at the end of page 2 for the problem I'm having with BB Bastard Frag Ammo feeding in certain mags.

Original issue: Try changing your hop up rubber. KA rubbers are known to be problematic.

Current issue: SHS nozzles are known to be slightly too long. File off about a 1/3 of a mm or put the stock nozzle back in.

Turn the gun upside down while the magazine is inside and try firing.

With no magazine in the gun, fill up the hopup with BB's, turn it upside down, and try firing with an unjamming rod in the feed hole to prevent them from bouncing out.

With the barrel removed, place the hop-up on the gearbox and see if the nozzle will reach at least half-way into the bb chamber, and clear or retract COMPLETELY out of the feeding hole where the bb's come up from the magazine.

First two will isolate that it is not a magazine issue, since it's still unclear if you have 1 or more unresolved issues.

The third will isolate the suspicions of a compatibility error with the nozzle.

there's your problem. shs nozzle is too long.

Also, gears are not supposed to be tight. They are supposed to have a certain amount of play on the axle.

Bad wording. The gears are not "tight". They spin freely, now with less lateral movement. Before there was a lot of side-to-side movement, it was evident in the sound of the gun when fired.

I'll try some of the mentioned tests and then maybe I'll change back the air nozzle.

Preliminary tests show that the shs nozzle is too long. I can see it peeking into the hopup chamber when retracted.

Feeding bb's by hand can be done, but I had to use my unjamming rod to push them in with more force than any magazine spring would supply.

Ill file down the nozzle as a start. Are there any negative repercussions to filing the end of the nozzle? Will it negatively affect my FPS?

Sounds like dirt mags but that's me.

Found that Dboys M4 mags and Cyma seem to feed flawlessly.

Try oiling your mag springs. Sounds like shit mags to me. If you've changed the bucking and hop up and it's still doing it then yeah the mags or it's the nozzle. The nozzle. You're using the wrong nozzle. I've done it. Took bad advise someone saying that an Mo5 nozzle and M4 are the same and they aren't even close. Only thing I can think of. If that doesn't work maybe the hop up is too close or not seated properly in the barrel.

Filed down the nozzle, it fires now. Just need to find a chrono to test the FPS, and run it for an extended period to see if it starts to double feed again.

The Nozzle I got was labelled as an M4 nozzle

every brand of nozzle is of different length. shs m4 nozzle is longer than average.

MP5 and M4 are different, however MP5K nozzles work in M4s.

As long as you have sufficient clearing when the nozzle retracts, you shouldn't have a feeding problem again. All signs/symptoms point to the nozzle. Glad you found the cause.

So I just put about 300 rounds through the gun.

My VFC Hi-cap works fine
My VFC Mid-Cap works fine
My King Arms mid-cap misfeed every 5-10 shots.
One of my MAG mid-caps misfeeds every few shots, I'll assume this is consistent with the 8 others I own...

If I recall, I only started having problems with my MAG magazines once I changed the stock handguard for an MK18 RIS. Is there any way this change could have some how thrown off the tolerance such that my MAG mags suddenly don't feed as well as they used to?!

Does the orientation of te mag make a difference? Only way your rail installation could have messed with anything is if your outer barrel is not seating correctly after you put on a new barrel nut.

Orientation of the mag? I just put the mag in and leave it. I added some velcro in the mag well to stiffen things up. Before I had some problems with mags not clicking in, especially the MAG brand. They would shuffle up and down a bit which obviously created feeding problems.

Shouldn't. As long as the barrel is sitting in the receiver as it is supposed to shouldn't be a problem. What I do is throw some silicone oil into mag and work the spring with an unjamming rod with the end cut off so it doesn't get stuck and work it that way. I only had bad feeds once. Using a G&P sentry and KWA mid caps. They fed like ass. Some mags just don't gel with some guns but like I said. The CYMA and DBoys mags always fed flawlessly for me