I just bought a Larue MBT trigger for my Form 1 SBR. Previously I had a Mil-spec FCG that came out of a bargain shop lower build kit. The lower reciever is an Anderson, and I have well over 5k rounds through the gun without issue.

I pulled the grip off, removed the safety selector/detent/spring. Installing the trigger assembly was a breeze and it dropped in without issue. Next, I went to put the hammer assembly in and it felt extremely tight compared to other builds and trigger installs I’ve done. Nevertheless I got it in there and proceeded to install the safety selector. At this point I noticed that the rearmost bar (safety selector interface) was raised significantly into the safety selector hole and I couldn’t insert the selector.

I figured no big deal I’ll just pull the hammer and install the selector first. That worked fine, but once I put the hammer back in it pushes the bar into the selector so hard that it will not turn whatsoever. I’ve double checked my springs and the installation and everything looks groovy. With the selector removed, the trigger operates correctly but it is an EXTREMELY light pull for a defensive carbine. Since this is my first Larue trigger I have nothing to compare against, but I would say the ‘normal’ spring pull is 1.5-2.0lbs.

Out of frustration I installed the trigger group/selector into another lower and it installed fine, but the trigger felt sloppy and the pull was much heavier. Maybe my lower is out of tolerance, but I really don’t want to switch it since it has NFA paperwork tied to it and a Mil-spec trigger has been working just fine for a long time now.

On a whim I bought another MBT with the TAC on the $99 sale the other day, and I had them include a Larue safety selector. My next course of action was going to be to install that trigger into the gun and see if it had the same problem, and then try both triggers with the Larue selector, and finally try them in the TAC to see if I notice any differences.

Anybody have any other suggestions?

Back out the grip screw a tad.....it may be slightly protruding into your fire control group "pocket" and pressing against the underside of the tail of the trigger....

Install trigger.

Install selector.  

Rotate selector to "safe".

Install hammer.



You may encounter trouble installing the hammer if the safety is in the the "fire" position.

And good point about the grip screw mentioned above.  If necessary, purchase a 1/4x28 cap screw at the hardware store that is 1/4" shorter than what you have now.

I never made it to installing the grip back, so we can rule that one out. Besides, the grip screw doesn't protrude into the FCG area whatsoever.

I can install the selector without the hammer and it rotates freely, but as soon as the hammer goes in the selector is locked down HARD. Again I was able to install this thing into a different lower and it functions, but it has all sorts of slop in it and feels worse than the original mil-spec trigger.

ETA: The trigger sits correctly without the hammer, even with the selector installed. When the hammer is installed it is pushing down on the front of the trigger and the trigger pin is acting as a pivot point which raises the tail of the trigger well over .100".

I had this with my Ruger 452 triggers in one lower. .... Seems like I had to file down the the top of the trigger where the safety rotates.

It was as if the bottom of the trigger well ( or what ever you call it) wasn't  deep enough couldn't tell for sure. All my milspec triggers and my Geissle worked but neither of the Ruger452s would in this lower. Both 452s worked in two other lowers.

I figured the simplest solution was to file(then stone smooth) the top(IIRC) and it worked. 

To add:
Don't think I tried it without the hammer. I was kind of disappointed with these triggers so I said fuck it and took the file to it.

I had the same thought but I didn't want to take a file to the trigger until I could verify that the lower was the root cause of the problem. Once I get my next package with another trigger and selector in it if nothing changes I'll probably break the file out.

Update:

My second MBT showed up and I finally got around to putting it in my gun. Fortunately, the installation went without a hitch and everything is back to good except with a much nicer trigger. Unfortunately, that leaves me dumbfounded about the first trigger. Here's what I know...

The first trigger didn't fit in my Anderson lower SBR. I experienced the problem in the OP.
The first trigger DID fit in a stripped Anderson lower that is a sequential s/n of the SBR, but it felt gritty.
The first trigger fits in a Larue T.A.C. and feels very similar to the second one thats currently in my gun.
I don't see any noticeable difference between trigger 1 and trigger 2, but there is a huge difference in how the trigger sits in my SBR.

What says the crowd? Out of spec trigger? Out of spec lower? Tolerance stacking between the whole thing?

I install the trigger, install the hammer, cock the hammer, and then install the safety.

Cocking the hammer should drop the rear of the trigger enough to slide the safety in.  If not, something is off.


I wouldn't file on the trigger tail, rather I'd remove material from the selector barrel until everything works properly.


If that's not an option or you don't want to, I'd send the trigger back for a replacement.



And not to be a dick, but I have never understood why someone would put a $200 stamp on a $40 lower.  I always figured the smart move would be to spend a little more on a better lower (Mega for instance) and then form 1 it.


ETA: I see you bought a second trigger.  My vote goes for tolerance stacking.

Ya know I can't help but laugh at myself for that exact reason... I'm not typically that dumb lol. I've got $3000 in the weapon (counting the can & stamps) and $39.95 in the lower...

I was at least smart enough to pistol it and make sure everything ran good before I put in the paperwork, but that was as far as it went.