I put in a brand new Upper Receiver, firing chamber, Bolt, and ejector plate.


I have put in a new Upper Receiver, firing chamber, Bolt (all new) and ejector plate. But...I still ahve PROBLEMS...


When I do MANUAL ejection tests (pull the charging handle back), the gun works PERFECTLY…it will eject 30 shells perfectly, with no problems. There is good power to the ejection, and No problems. Everything is PERFECT.



When I fire the gun however (semi) and (full auto), then gun fires and ejects the first round perfectly…but the 2nd round never goes off. So if it’s on (Semi), I fire once-shell ejects, bolt goes forward and loads the next one in the chamber, then I pull the trigger, and I hear a “click”…but nothing happens…since the hammer is now up, I have to open the upper receiver, and push the hammer back down, then eject the shell. These cartridges are all fairly new, and loaded the SAME way...properly lubricated, and with new caps. The cartridge that doesn't fire on the 2nd trigger pull, will fire after I push the hammer back down, and re-load...but then the next cartridge in line will not fire.



I have switched out the lower receivers as well, but get the SAME result.



Any idea what may be causing this? I have a MAJOR film shoot this weekend (Thursday through Monday) and would LOVE to have this gun fire once in a while.

Thanks so much guys!!

I'm sure some of our members with more experience on M-4 type modelguns will chime in soon.

My initial thought is that the bolt carrier is not getting into battery, thus the hammer will strike the firing pin when the bolt carrier isn't "locked" properly.

I'd spray it with silicon oil and work it in throughly. Or/and examine the moving parts carefully to see if there are any obvious marks of where there can be unwanted friction between parts.
Smooth out any abnormal wear point with steel wool or super-fine sandpaper.

My 3 cents...

And good luck

Hi Trev,

You're having no luck at all with this are you You'll know from our previous contact that I don't own one of these MGC M4s so I can't speak from personal experience.
There will certainly be other members here that are more qualified than I with M4s

However, trying to think through the sequence of events you describe, I'd suspect the hammer mechanism, or the sear. I guess there'll be an Auto-Sear in there too

Cocking the gun by pulling the charging handle back sets the hammer beneath the sear. When you pull the trigger, the sear releases the hammer so the gun fires that first shot.

Normally, certainly when in Semi mode, the recoiling bolt pushes the hammer back under the sear then re-chambers the next round.
Pull the trigger, the sear releases the hammer again to fire.

In your case, it could be that the sear isn't holding the hammer during firing. So, when the 1st round fires, the bolt's blown back, but as it returns forwards the hammer could be coming with it and stops resting against the firing pin.

The click you hear could be the sear mechanism moving but the hammer ain't there to be released.

In Auto mode, and I stress I'm guessing a bit here, when the 1st round fires, the bolt recoils, setting the hammer under the sear again BUT the Auto sear releases it to strike the pin hard enough to fire the second round. It should keep doing so till you release the trigger.

All I can suggest is that you set it in SEMI, fire once, then open the recievers. Best get some advice from an M4 owner to ensure it's safe to open the gun up at this point ... I wouldn't want you taking an eye out by a flaying recoil spring here...

The hammer SHOULD be set beneath the sear. If it isn't and you find it up in a position where it'd be resting against the back of the bolt, then my guess is your problem is sear related.

I hope this helps some. As I say, I AM guessing a bit here but I can't think of another reason. You've replaced everything else by now


Ah... just read 2sharp's advice, he'll know more about real-steel weapons than I so I'd steer towards his advice first

Trevor,
I am sorry to hear that you are still having fits with the M4.
Can you check to see:
After you chamber the round, can you move the bolt farther forward with the forward assist? If so, the bolt is not reaching full forward position and the hammer will strike the carrier too far away from the cartridge to ignite it. Perhaps there is some interference with the bolt carrier and the magazine? Have you tried different mags?

Thanks Jerrod--yah I have been going day and night over the M4...really taking it apart from the ground up. Last night I had my first successful firing. I got 5 rounds and then 8 rounds to eject on full auto... After replacing the upper receiver, bolt, all ancillary parts for the bolt, firing chamber and ejector plate, I replaced the recoil spring and switched magazines...I think the magazine may be a major culprit, as suggested...I am going to do some more tests, and I will let you know...hopefully things are looking up!