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View Full Version : Tutorial: HK Trigger Pack Semi-Auto Conversion



holescreek
11-27-2016, 09:40 PM
Here's another tutorial cut and paste from my hard drive. Rather than rewriting it in present tense, just understand it was written many years ago. The HK trigger pack is far superior to the Cetme pack design and can be tuned to give a very crisp 2 to 4 pound pull when worked over by a good gunsmith. If you are building a pack for 922r compliance you're going to need a US made trigger, hammer and sear. I just used the original parts for this tutorial. You can use an HK trigger pack even if you're building a Cetme as long as you use the safety lever from the HK too. Don't forget that switching between metal and plastic trigger housings requires the proper length safety lever due to thickness of the housings.

Now back to olden times:
Ive been doing some research on the HK G3 trigger pack. I took one apart for some optical scanning and figured that while I was at it Id do the SA conversion. There are a couple of threads already on the assembly but the instruction sheet for the conversion floating around the net is kind of hard to digest until you actually do the mod.

The conversion requires the usual cutting out of the FA component pin, a new hole for the SA sear spring, and another hole for a pin to block the trigger from the FA position.

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The 1/8 hole is extremely important!

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Without the 1/8 pin welded in the trigger can be pulled against the FA stop pin where the disconnect portion of the sear wont make contact with the hammer.

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The purpose for this study was for me to gain an understanding of how the HK trigger pack actually works. As usual, I did an optical scan of each of the components then moved them into CAD where I could manipulate them.

Step 1 - Cocked and locked (safety on)

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Step 2 - Safety off, Trigger pulled about 1/3 of travel. Bottom of sear just makes contact with the top step of the trigger.

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holescreek
11-27-2016, 09:41 PM
Step 3 -Trigger pulled approximately 2/3. Top step of trigger has lifted sear so it is about to leave the hammer notch.

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Step 4 - Trigger fully rearward stopped by the safety and the 1/8" SA pin. Hammer is released from sear and is fully forward. The sears internal spring plunger has pulled the sear forward off of the top step of the trigger onto the lower step. The sear spring installed in the semi-auto conversion (not shown for clarity) forces the front of the sear upwards.

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Step 5 - As the hammer is cocked the lobe on the bottom pushes down on top of the sear against the pressure of the sear spring.

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Step 6 - As the hammer continues rearward the front of the sear catches the hammer notch

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Step 7 - As the trigger is released the rearward pressure from the hammer and the sears own spring plunger pushed the sear backwards against the front of the trigger step.

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holescreek
11-27-2016, 09:42 PM
Step 8 - Trigger fully released and is resting on the lower trigger stop. The hammer is retained by the sear and the sear is fully rearward and is no longer in contact with the trigger.

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While I'm at it, I'll toss in some pics of my reassembly

Trigger, sear, trigger spring, and pin first. Make sure the trigger stop is above the lower stop pin in the cage:

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Next is the semi sear spring and pin.

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Hook the two individual ends under the hammer bosses:

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Next is the hammer and it's pin. Note: A US made hammer will have the front sear notch ground off and if you're making a SA conversion you will need to take care of this yourself.

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holescreek
11-27-2016, 09:43 PM
Then the hammer strut and spring:

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Lastly the ejector, it's spring and pivot pin

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When you get it mounted into the lower housing and have the safety installed double check the disconnector function. With the safety in the fire position pull the trigger and ease the hammer down slowly. With the trigger held to the rear, cock the hammer and make sure it is retained by the disconnector. Release the trigger and listen for the click as the sear leaves the trigger.

The pretravel adjustment turned out to be so easy I think everyone should do it just because they can.

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I used an M3 x .5 set screw 6mm long.

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