WE AK74un GBBR Bolt Catching/Jamming
 

Hi,

I'd like to see if anyone can help with this little problem.

OK, so I have a WE open-bolt system AK74un GBBR. Upon receipt it functioned perfectly.

After a few adjustments and tests it began to jam, the bolt jamming at the rear and requiring the charging handle to be pulled back and released to do so. This fault will happen with or without a mag inserted (i.e. just cocking it back via the charging handle will cause the bolt to remain back unless pushed forward) and seems to be more prevalent when pointed up as opposed to down.

I've stripped it and lubed it with no joy and examined all parts closely (checking for kinks/nicks along the rails of the upper receiver or along the bolt etc...) with no sign of anything pointing to the reason for this. It does appear that downward force on the portion of the bolt visible at the rear of the upper receiver and/or downward force on the charging handle will release the bolt forward.

So any tech-heads fancy throwing forward some ideas as what's a good idea to check next, I must point out that GBBR's are fairly new to me.

Any help would be gratefully appreciated.

90% of hte time i have a jam in an OB WE its the nozzle Oring jumping out of its groove and getting pinched by the piston, forcing the nozzle to stay fully extended, is hte nozzle sitting properly in the bolt when it jams or is it extended and sticky?

It was one of my guess, but when I look to the Oring, it's look good, at their place. I lube it and don't see any change. But I'will try to put it out, and check again.

I had it happen once, it could be the lugs or side of the rail is slightly deformed causing the bolt to get stuck at the back. If the sides of the receiver are slightly off spec, it can cause the bolt to jam at the back. I doubt it's the nozzle, but to be sure, remove the nozzle and manually cycle the bolt and see where the friction is. If it is the receiver sides, try to lightly hammer the sides/lugs out and retest

I open the GBBR. The O-ring look great, but I change it to be sure (2 times) and the problem stay.
I analyse more in detail and it's look to be a mecanical resistance at the middle of the run (the trigger assembly looks to do some restriction, but I don't know if it's normal or not. All the rails look straight too...).
I'm looking for a complete "How To" disassemble the AK74un but I didn't find nothing complete (trigger assembly, hop-up/barrel, the nozzle).

So I'm close to the starting point again

You can try to remove the trigger box/assembly and manually cycle the bolt to identify the point of restriction and to isolate the problem. I'm 80% sure it is the rails on the receiver where the bolt slides :)

I hope it's not the rails... but I don't know how to remote the trigger assembly and don't see any manuals or "how to" to remove it.

Open the top cover, there is a spring, rod with lock for pushing the bolt back. By pulling the bolt backward to see if between the rod and lock (close to the end)moving up and down. If too much space in between could cause bolt not moving freely. Use a piece of foil paper to fill the gap to prevent it wobbling up and down. Hope it helps.

Remove the top cover plate, remove the recoil rod and bolt. Remove the selector plate by undoing the grub screw that holds it into place inside the receiver. Remove the handguard by undoing the screw at the bottom, remove the pin that holds the trigger box in place.

If you determine that the rails are a bit tight causing alot of resistance, use a mallet and lightly hammer the sides causing the resistance.

I'will try this week. I'm more visual, but I think I understand.

Thanks a lot to al of you

I want to know, wich type of oil or gease do you use inside your GBBR ??

Some people tell me to put only silicon oil everywhere, no geace in rail, etc. but i'm septical

Either silicon oil or pool Oring grease for the o-rings and regular grease (not too much) for metal on metal movement.

I use lithium grease for all the mechanical parts (ie. hammer, sear, disconnector, bolt lugs/rails. I only use silicon oil for the nozzle oring.

I did a lot of work tonight.
What I do : bad work with the rail, I have to "undo" what I did
BUT I found the real problem!!!!
Hard to explain for me in english, but it's look to be the bolt guide and/or spring. It do a lot of friction inside the hole of the bolt. I tried to push this guide lower and it's work really better :) (but as I said, I misaligned uselessly the rail so there is a new FAIL problem).
So now I have to know how to fix the spring guide jamming problem (and I'll work on the rail alignement tomorrow).

Glad you found the problem, maybe you can take pictures and show us where the resistance/jam is. Hope everything goes well.