AR: Bolt not cocking hammer during live fire?

[Kind of Blued]

I moved fire control parts between three lowers for a few reasons and for some reason the hammer is not cocked after the first round fired. By way of a dry function check, everything works as intended. This is on a lower that previously had a two-stage trigger, but now has a single stage trigger.

Yesterday I was shooting my carbine with the substituted single-stage trigger and had the same problem. I'd insert a mag, load a round, turn selecor to "FIRE", fire a round, the bolt would cycle, insert a fresh round, but the hammer would not be cocked. During dry fire, every works as designed however. After this problem occured, I pulled back on the chaarging handle just enough to cock the hammer without ejecting the live round, and let it forward. This caused a two-shot burst (doublefeed?) that kind of suprised me, and I decided I'd try to figure it out before shooting it anymore.

Something I noticed is that the single-stage trigger group allows the hammer to be depressed to the point that it is flush with the lower receiver. Here's a photo:

The hammers on the two-stage triggers that came in my two RRA rifles can't be depressed nearly as far. Here's a photo of one of those:

I don't even know if this has anything to do with it, but I have some more photos if those would help you help me.

Does anybody know what might be going on?

Any help/ideas are very appreciated.

 

[Telperion]

The hammer is following the bolt home. Based on your charging handle slamfire incident, I'd venture there is insufficient hammer/trigger engagement. Are you mixing hammers and triggers from different kits?

Your rifle is UNSAFE and should be tagged out until the problem has been fixed.

 

[Kind of Blued]

The hammer and trigger were in a lower that I bought from a forumite here. He may come across this thread. I know he did some work on the trigger, but he may not have intended for it to be used in a semi-auto setting. It was previously in the lower that he (and now I) was using with a .50BMG upper.

 

[arthurcw]

Given recent legal events, be VERY CAREFUL where you take this gun to test it when you think you got it solved. Just Sayin'. CYA.

I know he did some work on the trigger, but he may not have intended for it to be used in a semi-auto setting. It was previously in the lower that he (and now I) was using with a .50BMG upper.

I would bet it's an unintended consequence of the FCG being customed to work on the .50. You may want to dedicate a lower to it specifically so you don't have any unhappy surprises (from you gun OR .gov). AR's are modular, but the .50 BMG uppers push the outer edge of that envelope from what I understand.

 

[Jackal]

Kinda sounds like short stroking to me.

 

[Bartholomew Roberts]

Kinda sounds like short stroking to me.

Except that if it was short-stroking to the extent the hammer did not cock, it would also not be loading the next round into the chamber.

Sounds to me like Telperion called it. The hammer is following the bolt due to insufficient engagement. This is definitely a problem you want to correct for both legal and safety reasons.

 

[Whitman31]

Sounds like the disconnect isn't catching, this would explain why the hammer will catch when manually depressed with your finger. Try depressing it with the trigger pulled. After the hammer cocks let go of it while still holding the trigger. When you let go of the trigger the hammer should click off of the disconnect and catch on the trigger, but not fall.

If this is the case, whoever played with the trigger took it a bit to far. It can be repaired with some blacksmithing, but I suggest a new set of parts including hammer, disconnecter, trigger, and springs.

 

[MythBuster]

Order a Rock River two stage and your problems will be over.

 

[Riss]

Yup needs proper function test. Pull and hold trigger, hammer drops. Cycle action, if hammer stays cocked then trigger should click on reset (forward travel) and then drop hammer when pulled again. Sear/disconnector possibly not installed properly, could just be the spring. Or could be a stacking of tolerances that are making it be "out" of adjustment. Sometimes the really tight triggers have issues when put into a slightly out of spec lower.

 

[Whitman31]

I did a custom job on my trigger and it's a tricky thing. If you add too much material to decrease the "take-up" then you run the risk of not having the hammer catch on the trigger. When the disconnect lets go. In addition, you can end up with a situation where the disconnect doesn't let go.

 

[Kind of Blued]

I DO have a dedicated lower for the .50, although I switched out fire control parts to have the better (two-stage) trigger in the .50 lower since I'll be shooting long range with it.

I think I will just buy another RRA two-stage trigger. It's not like there are any rifles around that I want a creepy trigger in anyway. Thanks for the help guys.

 

[strat81]

Smart move with the new trigger parts. A ~$100 trigger is much better than 5-10 years for possession of a machine gun.

 

[Kind of Blued]

It was a slamfire, but I'll introduce the trigger parts to a saw and the recycling bin anyway.

 

[Tarvis]

Sounds like the disconnector is not timed (caused from mix-matching parts) which can cause your gun to blow up if a round is fired while the bolt isn't locked. Get a JP trigger or have a gunsmith time it for you.