King Arms M4 tight selector switch
 

I have a problem with a new KA (7mm bushings) m4 that's been downgraded to shoot 350 fps.

Got it from the store and test fired and everything was working fine. Including the selector, went smoothly between all firing modes.

Since I usually upgrade my own gun, I wanted to take the gun apart and compare it to my TM m4.

Take down and reassembly went smoothly, but once I got the gun back together, the selector switch got very tight when moving from safe to semi, and gets worse from semi to full auto. I took it apart to find scratch marks on the circle part of the selector switch (the part that moves the selector plate on the gear box). It seems it was rubbing against the bushing on the gear box.

When I have the gear box in the lower receiver with no body pins, or the mag release installed, the selector works smoothly. As soon as I start putting things back on, the selector starts getting tighter and tighter. It looks like all the fittings are pushing the gear box to the left causing the selector switch and the bushing to contact. I can't figure out why this is happening and I'm ready to remove the selector and just grind down the circle until it fits. What kills me is that it was fine before I opened it! Any ideas would be much appreciated.

bump... anyone have any ideas? Asked on other boards and it seems like sanding is the only way!

I don't get why the gun was designed with such low tolerance! KA seems to make a pretty sturdy gun but damn it I wish the parts would fit properly!

You could be tightening the pistol grip screws too tight. Screw them in slowly and play with the selector until the screws are snug, but the selector still moves freely.

Awesome. I haven't gotten to the pistol grip yet and it's still tight with just the body pins and mag release in place. I'll try messing around with the pistol grip... Maybe I can use the pistol grip to recentre the mechbox.
Thanks for the tip!

took mine apart to downgrade the spring, reassembled it and the tight fire selector was fixed. Makes sense if it was over tightened pistol grip screws.


[EDIT: mine came that way though]

It came that way?? Weird.... Well glad to know you were able to fix it! I'll let you know once I get everything together

hmm.. i just put mine back together and now I have the same problem. It's fine til I tighten the pistol grip screws, and then it gets tight. Problem is, as soon as I put ANY tension on the screws, it tightens up..

Haha damn... And all this time I thought I was the only one! Haven't had time to put mine together but I have some ideas now that I've got more suggestions. Try playing around with the tightness of the stock and the pistol grip. I suspect it might be a balance between the pistol grip and the stock that will keep the mech box seated properly in the lower receiver.

I just hope the gun feeds well after all this! Im worried about mag alignment as well as barrel alignment now!

If you guys get it fixed please provide updates!

hmm.. this may sound really weird, but I was just looking at mine, and noticed the gearbox has 4 threaded holes. I dont have much V2 gearbox experience but on my A&K masada it only has 2 holes. Now, the holes didn't seem to line up absolutely perfectly with the grip. So I switched which 2 were being used to hold the grip on, and the selector is smooth as butter again. Theory: maybe that was twisting the gearbox a bit?

I'll play around with it some more.. The next 2 things I can think of to try are either mill down the blade on the selector switch, or swap the bearing there for a bushing and mill it down so it doesn't stick out past the outside face of the gearbox.


in the meantime, I figured I may as well order one of these too: http://www.airsoftparts.ca/store2/in...oducts_id=2136

Thanks for the update!

A friend and I discovered we couldn't get the receivers back together on the KA M4 unless we did the motor grip screws and body pins in a certain order. I forget which order it is now, but if you're screwing down the motor grip first and then doing the body pins after and you're having trouble with the body / selector switch / etc coming back together, try changing the order of operations.

I did body pin, mag release, then grip. That does NOT work. The spring on the mag release pushes the MB too much to the side. Gonna try another order.

Ok so I tried all the suggestions here and it seemed to work at first! However, once I put the upper receiver back on it's FUDGED! Seriously, wtf is with this thing?

Just bring it to a gun doc if you're having so much issues with it.

I had the exact same issue with my KA M4. I was forced to buy a new non KA selector switch. Your plate on the inside is too think. So either sand it thinner or get a new plate. This is where physicals stores are a must to you can check it against the old one.