M*CARBO Brotherhood

Trigger Creep Elimination

Got an email from mcarbo saying that I’m not active enough. I don’t like to talk unless I have something to say,so I’ll give it a shot.

There is a fairly simple way to eliminate trigger creep by removing material from the radiused surface adjacent to the sear contact surface on the hammer of the sub2k. This is a .250" radius and is concentric to the hammer pivot hole(they share the same center point). This is because the surface to be ground and the sear face have a similar relationship to that of a camshaft lobe and lifter on an engine, as was evident by the wear on the face of my sear. In my opinion, if it is ground flat, it will accelerate wear on the sharp edge of the sear. You don’t want this because eventualy it will cause inconsistant trigger break and probably, after a while, hammer drop or maybe even full auto. This is only my opinion, you can take it for what it’s worth.

I should first mention that I am a retired machinst with forty years in the trade, and I did this work on one of my milling machines. Please don’t roll your eyes in dispair just yet. This can be done on a drill press of reasonable quality, but requires a little different set up and is not as easy. Also, there is guy with a website called the ktgunsmith.com. He knows what cooks on this subject, but uses expensive jigs and fixtures that I can’t justify dropping the bucks for. Read his article on sub2k trigger creep before reading my stuff below so it doesn’t sound like a bunch of complicated happy crap.

What I did was face flat a 2"x2"x1/2" piece of aluminum and drilled and reamed a .125" diameter hole about 1/8" away from the edge, cranked the mill table to the left a couple of inches and pushed in a 1/8 dowell pin(you could use the kel-tek hammer pin or probably even a 1/8 roll pin). I then slipped the hammer onto the pin, took a short piece of 1/8" rubber hose and pushed it over the pin down against the hammer so that the hammer could rotate back and forth on the pin but not move up and down. Then, I put a 3/8" diameter fine grit dremel wheel in the spindle, cranked the table over about an inch away from the wheel and brought the wheel down so the bottom of the wheel was just below the bottom of the hammer suface. I then carefully cranked the table over until the wheel just barely touched the hammer surface to the wheel. Then I rotated the hammer back and forth on the pin until there was no grinding sound. I cranked the table over .001" and repeated the same process until I had removed .030" from the hammer surface, removing and checking progress frequently. I have a
tubing micrometer to check this, but calipers will work just fine. On my hammer I ended
up with .157" from the edge of the hole to the surface that I had ground. I then cleaned
it, lubed it and assembled the sub2k. I almost greased my shorts! The creep is so minimal,
that I had to close my eyes and slowly squeeze to even feel it. The pull weight on my
lyman pull gage said 4lbs.8oz. So I took the sub apart, flitzed every thing trigger,
including the face of the sear and the surface I had just ground, including the sear contact points on both the hammer and the sear, reassembled and now have a pull weight of 4lbs.2oz.
and a “glass rod” break, right at the wall.

If anyone is interested in doing this on a drill press I can post my idea for a simple jig
you can make. Also, depending on any interest, next week when my mill is freed up from my
present project, I can post a picture of the set-up I used. I’m only posting this now be-cause of the email I got from mcarbo.

All said and done, this mod, along with all the great stuff from mcarbo, the change from what it was to what it is, is more than I ever imagined.

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Wow @GinNC you must be in a good mood and away from all the hurricane stuff cos that was a lot! I’m still reading it. I’ll have to read it a couple more times. I’m no machinist (I couldn’t do the trigger job) but it’s still fascinating to read about. I’m know there’s guys here’ll really dig this. Thank you.

And I don’t think it’s a problem if you don’t talk too much, I think it’s more like you can’t buy too many MCARBO parts or something :thinking:

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Dang @GinNC thanks for sharing that, don’t hold back man that was a great bit of info you shared there. :fist_right::fist_left:

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Your very welcome. you don’t have to be a machinist to do this…seriously!

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@GinNC

Wow. I agree. That’s awesome. I have only read up to the gunsmith link but I just had to stop and post this.

I can understand not liking to talk much or not having the time to keep up with a forum. Although I have gone to other forums for info and guidance on various subjects, this is the only one I have ever had the desire to be an active participant and contributor.
(greatly due to its overall mission statement, ideals, philosophy,and goals combined with the exceptional membership and code of conduct.)

That being said, I encourage you to be a part as much as you can. Your post is a perfect example of the value as a member and the knowledge you have, to contribute to our members and the site itself.

Info like this is never a wasted effort here. The people here are interested, will put it to real world use, and appreciate it.

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Thanks, glad you liked it. I think I figured out how to post pics to better explain it. Gonna try it right now.


Cool, looks like it worked. Anyway, you can see that it’s nothing fancy. It’s just a flat block with a hole in it. those other holes are there from another project. A block of wood would probably work as long as it is very perpendicular to the dremel grinding wheel. Hope this clarifies things. This mod goes especially well with the mcarbo trigger bar.

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The engineer in me wishes I had your tools and patience! Great job.

Question, what difference does the McCarbo trigger bar make? I installed the trigger springs, etc. but not the bar. I prefer very little creep and am OK with my trigger as it is now but I can never seem to leave well enough alone. :nerd_face:

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@GinNC Thank you! @Boomchucker is right, some of us really dig this sort of thing. I have a drill press and would definitely be interested in a pic of your jig design. :+1:

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@mbecker908 the new trigger bar mainly eliminated the pre travel in the trigger pull.

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Thank you! And such a quick answer, I appreciate that. The trigger bar is my next purchase.

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@mbecker908 You’re very welcome, I think I should have said “greatly reduced” not “eliminated” the pre travel. I think you will be very happy with it. :smiley: :+1:

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Sure thing. I have a few projects needing completion. After that I can work something up. Just need some time.

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Same here as Trigger Happy. The only way I can see to reduce creep, is to shorten the sear contact surface on the hammer. The t.b. only takes the free play out of the trigger. Don’t forget about the reset failure on the t.b. Unless mcarbo has done the fix on their new batch, You’ll need that little radius mentioned elsewhere on this site. At least mine does.

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I understand now what you did. You changed the hammer. I just did change the shape of the hammer at the leading edge of, what I call the “hook”

making it just a bit more rounded. The big change came from what I only polished at the rear of the sear. I only polished it.

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Is this the edge you ground ?

I am having a hard time telling where you modified the hammer.

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I do not think the sub2000 could ever fire in the AUTO mode. There is no way for the trigger to delay until bolt would close. The hammer would follow the rear of the bolt which I doubt would push the fire pin…

I AM SOOOOO WRONG !!! And have modified my thoughts.I went to range today to test my work. Hit the trigger and in a flash 5 rounds went down range. I was prepaired for it and and abruptly STOPPED. I had 3 different sears with me and changed them out right there. The PMS collar made that possible! after that it shot so smoothly. That first in 3 months since last shot. I have amended my other posts.

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Sorry I haven’t got back to you sooner. I screwed up the forearm I was making for my ak and so it took me longer to make a new one. Anyway, tomorrow I should be able to post some pics of my jig idea. If the spindle isn’t real loose on your drill press(sideways slop) it should be a pretty easy project for you, especially if your press table has angular adustment. I’ll try real hard to get something posted tomorrow. By the way, I checked out your trigger group polish post. That’s some really slick work!

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That hammer follow that you mention is exactly what happened with my ktec su 16b, and it was brand new(back around 2003 or so when I bought it.). It would go full auto for 2 to 5 rounds.

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That’s not quite what I did. My sear isn’t changed at all other than polish. All I did with the hammer is shorten the distance from the face of the hook(where your arrow points to) to the center of the hammer pivot hole. Doing that shortens the sear mating surface.

Oh different gun. Have you had that happen with the S2K?