I got severely autistic and wanted to share how I fixed a bit of play that was driving me nuts with the KNS Picatinny adapter on my new 7.62x39 Gen 1 13 inch.
Tools & Materials Needed
- 0.004" brass shim stock (Amazon, ten bucks)
- Heavy-duty scissors, utility knife + ruler, or tin snips
- Sandpaper (400-600 grit) or file for edges
- Nylon/brass mallet
- CLP or gun oil
- Roll pin punch (3/16")
- Wooden dowel or brass rod (for removal if needed)
Steps
- Remove the old adapter and clean everything Drive out the roll pin. Tap the adapter upward/out using a dowel from inside the receiver. Clean off all old silicone residue with solvent + scraper . Degrease the adapter’s rear interface block and the receiver slot completely.
- Cut the shim blank Cut a roughly 2.5 cm square piece of 0.004" brass shim stock.
- Shape the shim (Upside-down T style)
* Test-fit the square against the rear face of the adapter’s offset interface block (the part that slides into the receiver).
* Leave about ½ cm overlap on each side.
* Bend the side overlaps ~90 degrees so they wrap around the sides of the block.
* Trim the upper portions of the side flaps (cut away the top part) so that only the lower side edges remain wrapped. The final shape when flat is like an upside-down “T”.
- Final trim and fit check
* The main body of the shim should cover the bottom ¾ of the rear face of the interface block, with the bottom side flaps wrapping around to cover the lower edges of the block below the gaps (leaving the middle gap clear for the roll pin).
* Bottom edge of shim should sit flush with the bottom of the block — no overhang.
* Smooth all edges with sandpaper so there are no burrs or sharp spots
- Install the shimmed adapter
* Apply a drop of CLP/gun oil on the shim and inside the receiver slot.
* Hook the shimmed adapter into the top of the receiver dovetail track.
* Push it down vertically by hand as far as it goes.
* Use a nylon or brass mallet to gently tap it the rest of the way until the roll pin holes line up perfectly. Make sure the shim doesnt ride up as block goes in.
* Drive the 3/16" roll pin back in (use a proper punch).
Result: The shim takes up vertical and horizontal play, creating a tight, solid fit.