MPX Hammer Pin Walking

[TFT_Guns_Up]

Hey Guys. I recently dropped a Timney MPX Single Stage Trigger into my MPX Carbine. I had it to the range for the third time today.

 

The first time a ran about 125 through it with no pin movement. Second time a few days ago about 250, and around the middle of the session I first noticed the hammer pin had moved to the right side of the rifle. And today I ran about 250 and the hammer pin walked in the same direction.

 

While I didn’t have any malfunctions, I’d like to know how to prevent this from happening. Both set screws are tightened down as far as they’ll go.

 

Thanks in advance 

[Smithcity]

Got the same MPX / trigger combination. After you install the trigger and pins, you really have to crank down those two lock screws with the allen key they provide. The screws are pre-installed in the housing, if they aren't tightened enough, your pins will walk.

 

Now...what is "tight enough", I don't know. Timney doesn't give you an in-lb spec. I would probably start with 20 in-lb and increase from there if they are still walking on you. I did it by hand "fairly" tightly and haven't had anything walk. I'm probably 3k-4k rounds into the trigger.

Edited August 5, 2018 by Smithcity

[SJMPCC022]

While I am not familiar with the Timney set up you are referring to, I have a few Velocity triggers with what I think is the same set up ?

 

One set screw goes straight down through the bottom of the drop in to push up on it to create force against the pins to prevent them from walking out.

 

If this is what you have, I like the system and think it was a good idea.

 

But, you need to look at a few things, and putting a 3" cheater bar on the allen wrench isn't one of them. If it takes that much force to keep the hammer pin from walking, you have something else going on.

 

Look at the pin diameter. Most drop ins use .154 diameter pins, mil spec AR pins are .156 diameter, and the holes in the receiver can be quite a bit bigger. If you got .154 pins with the trigger, try your mil spec pins. They will usually fit through the drop in trigger and will have less slop in the hole.

 

Another thing to try is take the top set screw out and loosen up the bottom one. See if you can rock the trigger group at all? It may be you are pushing up against the trigger pin only and not the hammer pin. If the two holes in your receiver are off just a bit this could be happening. You may have to use a pick or a small allen wrench to pull up on the front( hammer) end of the trigger group and tighten the set screw at the same time.

 

As far as tightening the set screws, all the downward force ( and upward push) comes from the bottom set screw. The top one is just a lock for the bottom one. The bottom one should be snug plus a little, the top one just snug. I mentioned this in a different post on here, it is a "feel" thing. If you don't know what it should " feel" like, have someone who does help you. Many bad things happen from over tightening things.

 

Good luck and let us know what you find. Regardless of the result, someone who reads it will learn something.

[TFT_Guns_Up]

Ok I went with KNS anti-walk pins, and I’m gonna Test it out sometime this week. I also tightened down the screws on the Timney Trigger. I’ll get a range report sometime this week

[SJMPCC022]

9 hours ago, TFT_Guns_Up said:

Ok I went with KNS anti-walk pins, and I’m gonna Test it out sometime this week. I also tightened down the screws on the Timney Trigger. I’ll get a range report sometime this week

Nice.

[biggulp]

Tighten down the Timney screws until the wrench doesnt turn freely anymore, then give them a slight "snug" (another 1/8th of a turn or so). 

 

 

 

Edited August 21, 2018 by biggulp

[Matt1911]

JP anti walk pins work great as well. That's what I use for my Timney. 

[TFT_Guns_Up]

On 8/20/2018 at 8:48 PM, biggulp said:

Tighten down the Timney screws until the wrench doesnt turn freely anymore, then give them a slight "snug" (another 1/8th of a turn or so). 

 

 

 

That’s what I was doing... And they still walked. I’m testing out the anti walk pins on Friday