Kp9 install. after a little fitment, the alg ultimate worked perfect. - ALG Defense AK Trigger Ultimate with Lightning Bow

Get out the jewelers tools and vice for this one.

The construction of the ALG trigger is leaps and bounds better than any AK trigger I have seen. The trigger drops right into the KUSA KP9 and the alignment is perfect. You will very likely want to take some metal of the hammer. I took quite a bit off the face of the hammer and mirror finished all parts that slide against metal. When installed properly, this trigger will function better than most AR and Gucci Glock triggers. This has been, by far, my favorite mod to my SBR KP9. Here is how I recommend you do it:

Install the ALG trigger into your KP9. Everything should it snug and you should be able to engage the hammer by pulling the trigger. You may also notice that the safety doesn't work yet. You will need the extra pin the ALG came with so the safety can engage, but I will talk to that later.

Put the bolt carrier back into the KP9 and try to pull the charging handle. You will notice that the bolt carrier is now being pinched my the ALG hammer and is no longer able to cycle freely and is likely hanging up on the bottom of the bolt. Take a sharpie and color in the top of the hammer so you can see exactly where the rubbing is occurring.

Begin grinding the rubbing area down. It will take some time. If you don't want to spend all night on it, you may want to use a grinder. I took approximately 2mm off the very top of the hammer and smoothed it out to make an "S" shape. Keep applying sharpie, and seeing where the wear is occurring. Keep taking metal off the hammer until the bolt carrier can travel back unimpeded by the hammer.

The bolt carrier rides on rails internal to the KP9. When it rides backwards, it reengages the hammer. The OEM hammer is quite a bit smaller and doesn't push the bolt upward by much when the bolt carrier travels backward. An unaltered ALG trigger will cause unnecessary wear to the rails inside your kp9. You are going to want to talk off enough metal to where the bolt doesn't feel overly tight. Try to get the the hammer grinded down to where it feels the same as the OEM trigger when you pull back the bolt carrier.

Once you are happy with the way the bolt carrier slides over the hammer, I'd recommend polishing the areas where metal slides on metal, to include the ramp on the back of the bolt carrier. This will help minimize wear in the rifle and make the trigger squeeze buttery smooth.

You will also have to install the roller pin that allows the safety to engage the trigger mechanism. After you hammer it in, you will have to file a little off the top so it will fit under the safety lever. Once you have the safety pin property set up, it will lock the trigger in place with extremely tight tolerances. The trigger will essentially be fixed in place when the safety is engaged.

It took a few hours to get everything situated with this trigger, but it's definitely worth it. It comes with a extra tention spring to increase the draw of the trigger. but both with and without are fairly light. I'd say you can change it from 3 pounds to 5 pounds, but I am just guessing. The trigger draw is only about 3mm and it resets at 2mm. The trigger does not have a wall and instead has a smooth draw that breaks right at the end of the 3mm draw. Its extremely easy to rapid fire this trigger. It just works great with the overall feel of the KP9. Highly recommended.