Issue with KJW M4 GBB locking up

[CavemanSean]

I've swapped out my plastic lower for a full metal (finally!) but now I have an issue.

there's a tiny pinch of play between the upper & lower, and that tiny pinch of play causes the m4 to lock up when firing.

So far I've been able to resolve this using electrical tape, but I shouldn't have to be doing that!! (don't know if its BECAUSE of the gap or not, but my guess is that little movement causes the buffer tube to not do its job, causing the bolt to not come all the way back...)

Any ideas would be awesome & greatly appreciated!

I have a video of the issue (or what I think is the issue) here https://www.youtube.com/watch?v=XySXdiYKh1I

[FirestormX]

I'm at work, so I can't watch the video, but is the problem basically that there's no blowback?
In other words, the upper receiver doesn't line up with your buffer tube, so the bolt carrier can't move back into the buffer tube?

Or is the problem more along the lines of the bolt not coming out of the buffer tube?

[daishi]

Yah the issue is with the bolt not being able to go back becuase it gets stuck on a tiny lip. That happens to me sometimes when I re-assemble my kjw but then I just open and slam it shut and the issue never comes up again.

From looking at your video, it actually looks like your pin that holds the body together looks too small and is allowing the upper and lower that small bit of play. is it the same with both the back and front? You could always email kjw and ask for a new one. That's just my opinion tho.

Also...what version are you using?

[CavemanSean]

Originally Posted by FirestormX

I'm at work, so I can't watch the video, but is the problem basically that there's no blowback?
In other words, the upper receiver doesn't line up with your buffer tube, so the bolt carrier can't move back into the buffer tube?
Or is the problem more along the lines of the bolt not coming out of the buffer tube?

to me it's that the upper doesn't line up with the buffer tube, causing the bolt carrier not to move back into the buffer tube properly

Originally Posted by daishi

Yah the issue is with the bolt not being able to go back becuase it gets stuck on a tiny lip. That happens to me sometimes when I re-assemble my kjw but then I just open and slam it shut and the issue never comes up again.

From looking at your video, it actually looks like your pin that holds the body together looks too small and is allowing the upper and lower that small bit of play. is it the same with both the back and front? You could always email kjw and ask for a new one. That's just my opinion tho.

Also...what version are you using?

Just the back is the issue, the front is nice and snug.
it's a v1 body with the v2 bolt

[daishi]

Well its probably the issue right there, the pin isnt big enough and is cuasing play at the back where the bolt meets the buffer. You could test out that theory by shimming the pin or the contacts so its snug....

The pin itself...is it snug with the hole in the receiver, and is it snug with the upper? YOu could always add material to whichever hole it is not tight in.

[CavemanSean]

Hmmm guess its off to the CanTire after work to see what I can find to shim it... wonder if I can find just a bolt that'll be nice and snug.

Any idea on the width of that bolt?


LMFAO
So I just sent KJW an email...

Delivery to the following recipient failed permanently:

service@kjworksusa.com

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain kjworksusa.com by kjworksusa.com. [173.201.29.131].

The error that the other server returned was:
550 Mailbox quota exceeded

----- Original message -----

Epic fail right there!

[daishi]

That's the nuub email, I'll send you a pm with the right one.

Don't spread it around or it will end up like that one and getting parts will be a right pain.

The pin itself is just about 7mm. All I have is an old ruler, but the holes in the upper and lower allow a bb to pass through with a 1mm gap, so 7mm is the best idea I can give you. You should check both set of holes in you upper and lower, and the pin itself. Either the pin is bad, or you got different sized holes....which would be bad news bears.

[CavemanSean]

Thanks, new email sent away.

Future refrence for anyone, (I was able to borrow a digital caliper from a engineer my co-worker knows) my pins measure 6.38mm (just over 1/4 inch) and the holes on my metal lower & upper measure 6.4mm.

so we are doing some extreme modifications unless KJW gets back to me by next month, we will be tapping the holes on the upper & lower, machining our own bolt to fit it perfectly & finishing it off with a nut.... HOPEFULLY it works when we do this, I'd hate to have to purchase another lower -_- lol

[audi_bhoy]

I ran into the same issue on my first KJW M4, I then put it back all V1 and bought a V2 brand new -.-

[CavemanSean]

my stock bolts where loose, so I put in 1/4" bolt & nut did it hand tight and its nice and snug and fires like a dream now. (at least its not locking on me atm)

I'm gaming it this Sunday so we'll see how it goes.