WE HK416 won't fire unless bolt carrier is slightly out-of-battery - FIXED!

[Mr. CoBalt]

I have a pretty-much brand new WETTI HK416 that has developed a weird problem. It operated just perfectly for awhile (under 500 rounds I would guess) but now the gun will consistently refuse to fire unless I use the charging handle to pull the bolt carrier slightly back (like under 5 mm - just enough to keep the handle unlocked). It will then fire as usual.

There doesn't appear to be anything broken in the trigger group/bolt group/etc but if the charging handle isn't pulled back then pulling the trigger will just cause the trigger to click and lock (because it's not being reset by the bolt carrier traveling backward). The gun has to be manually charged in order to retry. It's almost like the trigger hammer isn't hitting the gas release hammer properly/fully which is doubly weird because when there is no mag in the gun the hammer (? part 50 on the parts diagram) can be seen consistently pushing the actual gas-nozzle hammer (parts 59 to 64 - that little box in front of the trigger assemble) forward and into the mag well where - if there was a mag in place - it should then strike the magazine's gas release. Also, with the upper removed and mag seated in the lower, the trigger does indeed hit the gas release properly… and vents a full mag of propane in your face if you're dumb like me…

Anyways, sometimes, but not consistently, the gun can be made to fire by wiggling/pushing on the magazine which makes me think perhaps the bolt carrier is pushing the mag out of position such that the gas release hammer can't make contact. Anyways, it's a weird issue and I'm almost tearing my hair out because the gun is pretty much brand new.

Any clever people on here have any ideas/suggestions/pointers to GBBR gun techs in the Calgary area? Could this be part 66-related? What does that little bit even do and how would I get at it? Thanks in advance!

PS - That's the M4 parts diagram I linked to but I've compared it to my 416 manual's diagram and it appears identical in terms of the parts I'm concerned with.

[Mr. CoBalt]

Nobody's got any idea about this? Much sadness

[andrew5826]

Lube the bolt? I dont have much exp with M4 GBBS

[Mr. CoBalt]

Originally Posted by andrew5826

Lube the bolt? I dont have much exp with M4 GBBS

Yeah, I've taken the whole thing apart and lubed it up with 10wt silicon shock oil, plus using AI lightweight silicon oil for mag fills. It manually charges very smoothly, and is smooth when it shoots, but just won't do any shooting without the bolt carrier slightly back :/

[Mr. CoBalt]

With much thanks to the help and insight of -Trooper- the problem has now been fixed. It was indeed something incredibly easy but also somewhat non-obvious for anybody not previously exposed to the workings of the WETTI system (such as myself).

The issue was that the white plastic/rubber bracing piece of the bolt carrier (which is not shown on the parts diagram but the tube [piece 38] slides through it) has a tendency to work itself forward during firing. When it moves forward enough, the bottom of it catches and slows the hammer (part 50) as that part moves forward to strike the valve knocker. This interference prevents the components from making full-force contact and firing the gun. That also perfectly explains why if the bolt carrier was kept back a little bit it would allow the hammer to clear the plastic block and fire normally.

Here are some better pics of the part in question:
Overview (after fix)


Close-up


Fully-seated


As you can see from the middle close-up image, it has already begun to work its way forward again from my test firing. Haven't quite figured out how to totally prevent this while still leaving the components able to be disassembled (ie. no JB-Welding it) but -Trooper- suggested a loop of electrical tape just in front of it so that will probably be the next step. The last image shows it once more pushed back as far as possible.

The reason that it seems such an easy thing to miss is that unless you know that that part should be seated fully to the rear of the bolt carrier it has the appearance of always being in the "right" place. It is also secured in the bolt carrier in such a way that it looks like it really shouldn't move (and indeed, pushing it back into position took more force that would be expected) so I originally ruled it out, although it was nonetheless suspect.

Hope this helps out any other people with the same type of issue!

[El Cactus Loco]

most WE M4 users just remove that plastic piece because it does nothing. the purpose of it was to help keep the nozzle assembly centered in the bolt carrier (off-center nozzles are the #1 leading cause of ripped/torn o rings/seals in WE guns) but if you properly align your nozzle as explained on the WE M4 wiki, then you dont need this piece of useless plastic.

[m102404]

Mine did that a lot (especially after many disassemblies). A new one, if it has a tight fit, will usually stay in place for a long time...still worth checking though.

I drilled/tapped a hole in the side of my plastic piece and put a grub screw in there. Hasn't moved since.

[Mr. CoBalt]

Thanks for the info guys! Especially the mention of the WE wiki, lots of info to absorb there

[twistidpair]

I just encountered and resolved this issue!!!

Thanks guys... ASC forums are the best!!!