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M4 bolt lock back


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Hey all,

I'm wondering if I'm having a problem with my M4 or if this is somewhat normal.

If I press the cartridge drop button and pull the bolt back it will lock back but not very securely. For example, if I push the bolt knob forward slightly the bolt will spring back to battery. Is this normal? It seems like the only time it will fully locks back is if a round is on the carrier and then the bolt is pulled back. Then, even pushing on the bolt forward will not budget. I thought there was a way to lock the ball back regardless of whether or not there are rounds in the magazine or on the carrier. Am I doing something wrong?

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I think you are doing it wrong.


The only time the bolt locks rear is if the gun is slap-empty and the hammer is down (trigger pulled). Sometimes the bolt will hang (not lock) to the rear if there is a round on the carrier. There are reasons for this, but that is a whole other subject.


Hopefully some of the other members can chime in; what you have described doesn't make sense.

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Yes, thank you. I searched a bit more and realized i was thinking of this more as an AR in terms of bolt function and that it would lock back anytime it was pulled back (obviously without a bolt catch button).

I think i was referring to what you mentioned as hanging.

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When you press the shell release button, a shell ejects from the magazine tube onto the elevator. You then pull the charging handle to the rear to chamber a round. The bolt should not be locking back. What you are experiencing is the bolt carrier hanging up on the hammer or the breech latch. I've noticed this effect if the weapon is dirty or under lubricated. Also if you're babying the bolt carrier, it will stick. The bolt carrier rails should be sloppy wet. Lubricate the crap out of the area the hammer rides against the bottom of the bolt carrier. Lube the crap out of the receiver extension too.


*Another remote option is deformation of the bolt carrier due to battering from the pistons. This event is limited mainly to the 11703 models with the 4 port barrels. These deformed bolt carriers would bind in the receiver when being pulled to the rear. A quick visual check of the bolt carrier where the pistons contact the carrier will let you know if it is the issue or not.

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Got it. Yes, it was only sticking a bit if i pulled it gently and tried to get it to stick. I wS forgetting that for any kind of breech reload you will still have to have a finger on the bolt latch to keep it back unless it is empty.

And i agree with the lubing. I am a SIG guy when it comes to handguns and am now convinced that using slide glide or another light grease is the best thing for metal to metal sliding/contact points. Grease sticks and stays where you put it so you do t have to worry so much about that grinding that eventually leads to wear.

Edited by Macfly
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