Aero Precision LPK

[whoknows]

So I started my ar build a while ago and I completed it last month. In my search to save a little money I found an Aero Precision lower parts kit on ebay for cheaper than anywhere else. I've shot probably a hundred rounds without a problem, but then today it started acting like I had it set on three round burst. After than happened I cleared the firearm and took it inside to check it over. With the lower separated from the upper, I pulled the hammer back and squeezed the trigger to simulate firing the firearm. I kept the trigger pulled back and reset the hammer to the cocked position then I slowly released the trigger. While I was slowly releasing the trigger, the hammer moved forward. So I was able to simulated two shots with one trigger pull. I checked to make sure the hammer spring was in its correct location and it was. My friend happened to have a dpms trigger group laying around that he lent me.

Here's a picture of the trigger group that I removed from the lower.


If anyone has any input on why this is happening and how to solve the problem, it would be awesome.

 

[rob63]

It sounds as though when you began releasing the trigger the disconnector was releasing the hammer before the trigger had traveled far enough to engage the hammer. Perhaps when you installed it the little coil spring inside the trigger that goes under the disconnector was kinked a bit and after firing the 1st 100 rounds had moved just enough more that the disconnector was no longer functioning properly. Just a guess, unfortunately, it is one you can't really check once you have disassembled it. You can try reinstalling it while paying attention to make sure that spring is in the right place to see if it fixes the issue or not, at least then you could rule that out if it doesn't work.

 

[whoknows]

Thanks, I will give that a shot later on tonight or tomorrow.

 

[CountryBoy19]

As stated, it does sound like the disconnector is releasing before the sear can engage. It's normal for a small amount of forward movement when the disconnector (further referred to as disco) releases, but the sear should catch it. If there are only a few possibilities.
#1 (least likely) is the sear surface is deformed. Does the hammer engagement on the sear seem solid if the hammer is cocked with no pressure on the trigger? If so we can rule this out.
#2 Disco spring not installed properly or not functioning properly. The "fat" end of the spring should be installed into the trigger. Many people don't even realize that the spring is different from end-to-end and is only to be installed one way. If it was installed wrong then reinstalled properly the spring could be damaged. If it is installed wrong currently reinstalling correctly should correct the problem if nothing is damaged.
#3 Worn/deformed disco surface; is it just me or does the hook on the disco look a bit "different"? Compare the shape of the disco to that of the DPMS kit. They should be very close; part particular attention to the hook part.
#4 Out of spec parts: sear surface in the wrong area, mis-shapen parts, could be anything letting the disco release before the sear engages.

 

[whoknows]

Sorry I havent had a chance to reinstall the trigger group. I checked to make sure the little spring has the fat end down, which it does. I takes some force to pull it out, and push it down. The disco does have blemishes on it, like knicks or some blueing that worn off. It didn't look like that when I first installed it. Im kinda leaning torward the disco being out of spec, its the only thing that looks like it could be wrong.

 

[CountryBoy19]

Sorry I havent had a chance to reinstall the trigger group. I checked to make sure the little spring has the fat end down, which it does. I takes some force to pull it out, and push it down. The disco does have blemishes on it, like knicks or some blueing that worn off. It didn't look like that when I first installed it. Im kinda leaning torward the disco being out of spec, its the only thing that looks like it could be wrong.

View attachment 47854

I think your next step is to remove the disco from the DPMS kit and lay them over the top of one another. The critical dimension is from the hole to the tip of the hook. If they are the same or very close then I doubt that is the cause. The hook angle on yours looks "off" to me but a picture of them overlaid on one another would be great. If it is a dimensional problem I'm certain Aero Precision will take care of you; they have been top-notch every time I've dealt with them.

 

[whoknows]

So i removed the dpms trigger from the lower, and noticed its set up completely different from the aero precision.



I've tried to contact Aero Precision, but havent heard back yet.

 

[rob63]

That's a 2-stage trigger, it tells you nothing about your aero lpk. Have you tried reinstalling your hammer and trigger while paying attention to the spring yet?

 

[whoknows]

Sorry, I have not. I will definitely do that tonight.


Edit:

SO I reinstalled the Aero trigger group, and I made sure the little spring was correctly installed. Its still has the same issue, just not as frequent. Even tho they prolly don't help, here's a few pictures

 

[whoknows]

Aero precision was nice enough to send me a new parts kit. I haven't had a chance to shoot the rifle yet, but so far it hasn't acted up on me doing the same tests that I did with the other trigger group.

Thanks for your suggestions

 

[rob63]

Aero precision was nice enough to send me a new parts kit. I haven't had a chance to shoot the rifle yet, but so far it hasn't acted up on me doing the same tests that I did with the other trigger group.

Thanks for your suggestions

Glad to hear it.