Umarex/Walther/Colt M4 Trigger-Updated pics!

[brassburnz]

****WARNING-THIS THREAD IS FOR INFORMATIONAL PURPOSES ONLY. IF YOUR UMAREX IS BROKEN OR IN NEED OF REPAIR, RETURN IT TO UMAREX FOR WARRANTY WORK***

Planning a trip to Angeles today, but my son said, "Don't take the Colt clone. I hate that trigger." We've put around 700 rounds through it, and the trigger has gotten progressively worse. It feels like there's a build up of debris someplace, so I decided to see if there's a quick fix just to make it shoot like it was new.

Sorry-no pics. I was still in the exploratory mode and didn't want to stop my train of thought. Will post pics later. Pics up now!

Loosened the flash hider, removed the pins (rear pin is still a pain to remove-requires a brass bunch and a small hammer), and separated the upper from the lower. Noticed for the first time that the tube for the stock is screwed into the lower. The castle nut is cosmetic only. Don't crank on it or you'll break something.

I finally figured out how to remove the trigger group.
1. Remove the mag catch.
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2. Remove the safety switch. It just pops out. It's held in place by a detent ball.
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3. Remove the safety indicator on the right side of the receiver. There will be an opening when you remove the safety switch. You'll see a small wedge shaped opening. Take a small pin punch and push through the opening. The safety indicator will pop out. It's also held in place by a small detent ball.
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4. Remove the pistol grip. This is what really holds the trigger unit in place. You'll need a long hex wrench and something to turn it with unless you have a T-handle hex set.
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There are four screws that hold the two halves of the trigger group together. All four of the screws were loose. I checked the trigger/sear engagement and saw that grease had attracted a lot of dirt onto the surface of the sear that engages the hammer. The trigger/sear sort of wobbled because the 4 screws were a little loose. I tightened them down just a bit, and the trigger actually felt better, but I'm not sure exactly how much. I didn't measure the trigger pull before or during.

I didn't really feel like taking the entire trigger housing apart, put I decided to loosen the screws. I loosened them to the point stuff started shifting around inside. When the sear wouldn't engage the hammer, I decided to close things back up since I did want to go to the range today.

I cleaned as much of the gunk off the sear and sprayed the engagement area with compressed air. The gritty feeling was gone, but the engagement surfaces of the hammer and sear were still pretty bad.

I decided to try something I learned from working on 1911's. After doing a trigger job, sometimes there are small burs or grit from stoning on the surface of the sear/hammer. To remove this without taking the gun apart again, you can "boost" the hammer a couple of times and this takes care of it. You put added pressure on the hammer then squeeze the trigger.

On the Umarex, there's a trigger strut/spring guide combination that protrudes into the pistol grip. With the pistol grip removed, this strut actually moves below metal housing. I put some doubled up Cue-tips in the housing so the hammer didn't hit, then pushed down on a piece of wood with the trigger strut. This makes the trigger pull super heavy, because you need to overcome the added pressure. I did this about 4 times while inspecting the surface of the sear. The sear engagement area started getting that polished look and the trigger pull felt better. Exactly how much better is difficult to say, but better.

After we get back from the range, I'll be able to give a better assessment of the trigger.

Here's something else I learned. When the trigger housing is out of the frame, the rear pin pops in and out very easily. But when you attach the pistol grip, the rear pin gets tough to move. I checked to see if there is contact with the lower but there isn't. These is a detent in the trigger housing that holds the pin. When you loosen the pistol grip, the rear pin moves much easier. The manual should say, "Loosen the pistol grip before removing the rear pin." This isn't as strange as loosening the flash hider. At least the pistol grip is attached to the lower. The grip screw doesn't affect the rear take-down pin. It's the diameter of the hole on the upper. Mine is a very tight fit. And it doesn't seem to matter whether or not the flash hider is tight or not.

[Seesm]

There is for sure some weird quirks on this rifle.

I still can not figure why they did not make the bolt release a "working" one but it is a neat little plinker...

I am sure when we get one we can work it out and make it work flawlessly like most of our AR style rifle's

[Touchdown456]

Brass,

I should've looked here this morning first. Didn't know you posted this, and I also went to work on my trigger today. HA, if I had read your post, it might have saved me an hour. But, I did go a bit further than you. I did unscrew and seperate the halves. When I did, suprisingly the trigger group actually stayed in place. That is, until I messed with it. Then, like usually happens to me, the springs went flying everywhere. Being how everything was apart, I took to cleaning it all. Took a little while to put it back together but eventually I got it. In the end, I didn't notice much difference in the pull. So, I'm still gonna send it out.

[brassburnz]

Brass,

I should've looked here this morning first. Didn't know you posted this, and I also went to work on my trigger today. HA, if I had read your post, it might have saved me an hour. But, I did go a bit further than you. I did unscrew and seperate the halves. When I did, suprisingly the trigger group actually stayed in place. That is, until I messed with it. Then, like usually happens to me, the springs went flying everywhere. Being how everything was apart, I took to cleaning it all. Took a little while to put it back together but eventually I got it. In the end, I didn't notice much difference in the pull. So, I'm still gonna send it out.

I figured the springs would pop out once the two halves were separated. I just didn't want to deal with that yesterday. Now that I'm back from Angeles and don't plan on going shooting for a couple of days, I'll take the trigger group completely apart and take a closer look at the trigger/sear engagement. From what I could see without taking it apart, it looks pretty straightforward.

I will polish the engagement surfaces of the sear and hammer until they are smooth and shiney. I may clip a coil off of the hammer spring or look for some reduced power springs from either a J-frame Smith or a Ruger revolver. I'm sure I can find something that will fit. I also think the trigger return spring can be lightened a bit.

The other thing I noticed yesterday is the stud on the trigger that gets blocked by the safety can still contact the safety cam even in the fire position. It doesn't always do this, so I think the trigger pin needs to be shimmed.

Also, if the safety lever is not rotated all the way horizontal to the "Safe" position, pulling the trigger can make the safety move to drop the hammer. When the lever is vertical, it happens all the time.

I'll be posting pics after I disassemble the trigger group. As far as voiding an warranties, there weren't any seals or pre-marked screws to break. Also, the four screws that hold the two halves together had loosened up quite a bit after several hundred rounds. I think Umarex needs to tell people to check them periodically. I don't think they'd loosen to the point of malfunctioning because the lower receiver holds them together, but it could make for a really sloppy trigger.

[IsaacGlass]

Nice going Brass, looking forward to your pic's

[brassburnz]

FOR INFORMATIONAL PURPOSES ONLY--DO NOT TRY THIS AT HOME

This is how the trigger housing looks after removing the right half. Be very careful because the sear spring, trigger return spring, and hammer spring are still under tension. They can and will fly out and you'll risk losing them, making your M4 a paperweight.
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This is the sear, disconnector, and trigger separated into parts. You get a really good view of the sear spring (the longer of the two) and the trigger return spring.
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This is what the hammer and sear engagement looks like outside of the gun. When working on 1911's I have a jig with the sear and hammer pins in their proper place. I also have a set of pins I can place in my frame that let's me check the hammer/sear engagement outside of the frame.
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This is the surface of the sear that could use some polishing.
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[brassburnz]

THESE PICS WERE TAKEN BEFORE I POLISHED ANYTHING.

This is the engagement surface of the hammer that can be polished. I polished the engagement surfaces of the sear with crocus cloth and oil. I polished the surface of the hammer hook with a hard Arkansas stone and oil. I didn't remove any metal, just polished the surfaces until they were shiney. That's it. The trigger smoothed up quite a bit, although the creep and overtravel are still there.
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The other pics are just FYI. It's nice to know what's going on inside the trigger housing.

This is the safety.
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These are the detents for the rear takedown pin and the safety. They are identical.
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This is the buffer that sits on the top of the trigger housing.
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[IsaacGlass]

Brass nice pictorial, Thanks

[Touchdown456]

Great pics. And anyone reading this, take notice of his warning. Being how I also lost my springs for quite a while (although I did also get them back and spent 2 hours reassembling), it is a good way to make your gun inoperable.

That being said - Brass, what kind of oil did you use on the sear?

[hkdad]

awesome write up randy!

[brassburnz]

Great pics. And anyone reading this, take notice of his warning. Being how I also lost my springs for quite a while (although I did also get them back and spent 2 hours reassembling), it is a good way to make your gun inoperable.

That being said - Brass, what kind of oil did you use on the sear?

I polished the sear with crocus cloth and Rem Oil on a flat sheet of glass.(I use an old aquarium turned upside-down.) I didn''t want to take off metal, just polish it up. I used a hard Arkansas stone and Rem Oil for the hammer hook. Again, just polish, no metal removal. The geometry of the engagement surfaces on my Umarex look correct. The surfaces were a little rough. I decided not to use any lube on the hammer/sear engagement.

Sometimes I will use a little dab of Tetra Gun grease (It looks like the same grease used by the factory.) on the hammer/sear engagement of my 1911's, but I decided to leave it dry on the Umarex. .22 rimfires are just too dirty and the grease attracts powder residue.

[GM4spd]

Good work,Randy, great intel, Pete

[piglith]

Nice work

[alain209]

just drosd my colt m4. thanks guys for the update.

[brassburnz]

Now with updated pics.

I adjusted some of the pics to show more detail. They were a little on the dark side, but I lightened them and now you can see the detail better.

The bearing surfaces of the sear and hammer are also easier to see.