KP-9 Archives

Since Kalashinkov USA introduced the KP-9, I’ve had a handful of guys ask me to make a quick takedown pin for it. Well, it turns out it is a unique size and the hinge pin would need to be around 3.75mm – smaller than what any of my vendors could reliably hit. My existing pins all have a diameter of .156″ or about 3.96mm so they would not work.

So, what to do? I’d bought a KP-9 with their brace and it was a nice weapon in terms of fit, finish, and operation. I’d pressed out the unique hinge pin and saved it so I could have replaced it but I decided to go another route. By the way, the original pin was swollen at the ends from being set but the middle measure 3.75 so that’s the number I was going with.

There’s the hinge pin between the rear sight and the start of the dust cover rail.

There is a spring on the pin to help the dust cover pop up when the recoil rod is pushed in. Note, the fitment of the cover to the rear sight block and rear trunnion is very good. If it weren’t for the spring, the cover would stay down. By the way, the big black round thing you see on top of the barrel pin has a groove behind it. When the brace is swung into the folded position, a tab on the brace goes into the groove and holds it in the folded position.

This is the original hinge pin and the spring that pops the dust cover up. The pin is 2.75mm wide and about 24-25mm long – mine measured 24.31mm after I pressed it out. Some deformation would have occurred when it was pressed in and the ends flared open.

How To Remove The Original Pin

I used a punch on my air hammer to pop the old pin out. You could also press it out or drill it out.

I used my ATS air riveter to pop out the pin in a matter of seconds. You could press or drill out your pin.

Reaming the Hinge Hole

If you look at the hinge, there is enough material around the hinge pin material to ream it out a bit. I decided to get a 0.1563″ (3.97mm) cobalt reamer and a 4mm cobalt reamer. My thinking was to first try the smaller reamer and if that proved to be too small, I’d step up to the 4mm (0.1575″). I bought mine from McMaster-Carr but you can get them from any reputable vendor.

Reamers are cool – they make perfectly round holes and you can do them in a hand drill if you are so inclined, which I was. Secure your weapon in a vise so it can’t move, use a drill bit or other pin to align the hinge parts from the other direction. As you ream, this slave pin, or alignment pin, will be pushed out of the way as a reamer’s head is blunt.

Put your reamer in your drill chuck and coat it with cutting oil, then slowly insert the reamer into hole – let it cut – don’t force it. You’re not taking off a ton of material so I reamed the hole out in one go.

The slave pin did it’s job and I had a true hole in the end. Okay, the .1563″ reamer’s hole worked but was too tight – If you don’t intend to pull the pin much, it would work but it was not what I wanted. I then did the same thing by inserting a slave pin but this time used the 4mm reamer and it worked great.

You see, getting the hole size right matters a great deal compared to some weapons such as the M92 and Krinks – they want to cam the cover up so there is tension that locks everything in place. With the KP-9, the fit of the dustcover relative to the rear sight block is so good that there isn’t tension so you need the quick takedown pin to fit snugly and the detent ball to do its job.

Our AK-V pin fits great. This is with the 3/4″ ring installed.

Here’s the full view of the hinge. Note the detent ball on the pin that keeps it from accidentally sliding out of the hole.

The way a quick release pin that has a ball bearing detent works is that a spring is behind the ball bearing pushing it up but it is captured in the hole. By sticking up, the ball bearing limits travel. Having a circular surface if you pull hard enough during extraction then the ball bearing is pushed down, the pin pulls free and then the spring pushes the ball bearing detent back up once it is clear.. Insertion is just the reverse.

In closing

I really like how it turned out. For folks who want to add a quick takedown pin, just order the AK-V pin [click here to open that page in a new tab] and then ream your hinge open. Note, you might want to get the same size reamers and see which you prefer – start with the smaller one first of course.

The pins make removing the dust cover really easy.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.