Help me figure out why my new LaRue MBT is sticking/doesn't feel right

[gregr507]

So I just installed a MBT in my AR, but am running into issues. I first installed with the heavy spring, but it felt really heavy, like far heavier than I imagine it is supposed to. It also felt gritty. I uninstalled it, greased it, and reinstalled it several times, but kept running into the same issue. Eventually I decided to try the light spring, which feels much better and closer to what I imagine it should be like. However, there still seems to be some grit/resistance during the first stage. Interestingly, I didn't notice it yesterday when I first installed it and though the trigger felt great, but today it feels heavier and grittier.


Another issue is that the trigger does not want to reset on its own, and also is sticking. What I mean is that when I pull through the first stage and approach the wall of the second stage and then let off the trigger, the trigger will stay stuck in that position and will not reset to neutral without me having to push it forward. Then when I try to test the reset, the trigger will stay stuck fully depressed, and will not reset unless I push it forward.


I've uninstalled and reinstalled this thing probably 5 times now (around 4 were with the heavy spring, then the last was the light spring) and keep running into issues. I feel like I am installing it correctly, is there something I am missing? What could be causing this?

Any help or advice is much appreciated

 

[scottka]

Make sure you have your trigger spring installed correctly. Look it up online (video or picture) and make sure the orientation is correct. It’s easy to mess up if you’re not comparing it to a picture if you’re not used to doing it.

 

[gregr507]

Here are a couple pictures of the trigger installed in my lower, hopefully that helps

edit - Here's a link if that's easier to view - https://imgur.com/gallery/2O5K2M6

 

[Bigtanker]

Here's mine.

 

[Hop]

I have a few and they all feel the same. I'd hate to think you got a bad one but everyone puts out a lemon once in a while. I'd call them and explain what it feels like.

 

[cmann250]

I had this exact issue with this trigger in one of my lowers. It was an off brand billet lower (probably not in spec) that had been ceracoated (pushing the fire control pocket further out of spec).

Emery cloth cleaned mine up. Do you have another lower compare to?


Sent from my iPhone using Tapatalk

 

[gregr507]

I had this exact issue with this trigger in one of my lowers. It was an off brand billet lower (probably not in spec) that had been ceracoated (pushing the fire control pocket further out of spec).

Emery cloth cleaned mine up. Do you have another lower compare to?


Sent from my iPhone using Tapatalk

Unfortunately I don't, this is my only AR at the moment. It's a PSA lower

 

[TJ Kackowski]

I had the same resetting issues with my MBT.

After removing the upper and a thorough examination of the lower by all assembled at the range and finding nothing incorrectly installed, it was suggested to "hit it with some WD40". I'm not a huge WD40 fan, so opted to use a few drops of gun oil ... one drop on each side of the trigger and hammer pins ... then worked the trigger for a few minutes. Voilà! Everything was working as expected. Reinstalled the upper and got to work.

As far as feel ... damn, LaRue makes a nice trigger. Until this trigger my most advanced trigger was an ALG ACT, and that feels really nice ... but the MBT ... wow!

I'm thinking I might need to add a small bottle of WD40 to my range bag and replace the rest of my triggers.

 

[gmcttr]

...so opted to use a few drops of gun oil ... one drop on each side of the trigger and hammer pins ... then worked the trigger for a few minutes. Voilà! Everything was working as expected...

Agreed...that trigger group looks very dry (and way to clean,lol).

A drop of oil at each pivot point (which should also lube where the hammer and trigger rub against the lower) and a dab of grease on the disco catch points and trigger/hammer sear and your problem may be solved.

 

[gregr507]

I did grease the points suggested by the pamphlet that came with the trigger, maybe I didn't use enough? I can try to take it out and relube it, but I did that already a couple times. Couldn't hurt I suppose

 

[Ggreen]

I've seen this on out of spec lowers. The mbt's are supposedly tested prior to packing. It's this the first trigger you've had in the lower?

 

[gregr507]

I've seen this on out of spec lowers. The mbt's are supposedly tested prior to packing. It's this the first trigger you've had in the lower?

The only other trigger I've had in the lower is the PSA EPT, which worked without issue

 

[gregr507]

So I disassembled it again, this time greasing the trigger hole in the lower and the sides of the trigger, and it feels much better. There's still a little grit in the first stage, but it resets normally now and the pull weight feels more like what I would expect, although maybe still a little heavy and it feels like it might be getting heavier as I try to work it in. Sounds like maybe the trigger hole in the lower might be scraping the trigger? I will probably try filing it a bit, but I can't tell exactly where it's making contact. This might be a temporary fix, but it would be a pain to have to keep regreasing it there every time.

 

[AngryRooster]

When you got your trigger did it come with the plastic test lower? I've ordered 3 and 1 came with it. If you want I can send it to you. Install your trigger in it and see if it's different than your lower.

 

[Hop]

Don't file anything yet. I think I still have a new in package one somewhere. We're both in the Fishers area I think. Maybe we can swap in some parts to see if you got a lemon.

Using Tapatalk to annoy my INGO buddies cameramonkey & churchmouse. Hi!

 

[masterdekoy]

Had the same issue with my MBT. Seems Larue makes them to very tight tolerances. So if your lower is on the tight end of the tolerance window (or if the trigger pin holes are slightly crooked) the trigger will stick because it rubs on the inside of the lower. I solved my problem by putting it in a different lower. Without that option, you would either have to file off a bit from the sides of the trigger or open up your lower a bit.

It should be pretty obvious where it is rubbing, if you look on the inside of the lower do you see shiny spots around the trigger pin holes?

 

[Hohn]

So I disassembled it again, this time greasing the trigger hole in the lower and the sides of the trigger, and it feels much better. There's still a little grit in the first stage, but it resets normally now and the pull weight feels more like what I would expect, although maybe still a little heavy and it feels like it might be getting heavier as I try to work it in. Sounds like maybe the trigger hole in the lower might be scraping the trigger? I will probably try filing it a bit, but I can't tell exactly where it's making contact. This might be a temporary fix, but it would be a pain to have to keep regreasing it there every time.

AR Triggers: lots of grease, NEVER CLEAN. The more carbon gets in with the grease, the better.

 

[gregr507]

I tried filing the trigger hole in the lower and a little bit on the trigger, barely at all really. I also greased the trigger hole, and now it seems to be working much better. No more sticking and it feels pretty smooth. I have the heavy trigger spring in there now, and ordered a trigger pull gauge to see if it was where it was supposed to be. Right now the first stage with the heavy spring is around 3 lbs, and the 2nd stage is around 2 lbs, for a total of about 5 lbs trigger pull. I actually like the light spring better from what I remember, but haven't yet changed it back in to measure the pull weight. The heavy spring feels just a bit heavy to me, and I liked the light spring because the wall was a little more perceptible since the first stage was lighter. I seem to remember reading people online saying the heavy spring was a bit lighter than mine, which seems to break around 5 to 5.5 lbs, so I'm not sure why that is. It does feel much smoother now though, so overall I'm pleased