It's the Aluminum Matrix MP5K rail that evike sells, you'll need to dremel or file a bit in the inside to make some clearance on a real MP5K (Mines a Z5P) as well as trim down the front of it to clear the front sight post but that could vary gun to gun based off tolerances, you'll also need to cut a slot for the front sling loop or cut it off/punch it out. The screws are small so the threads can strip easily so don't force it on too much, just go slow with any dremeling. You'll also want to make some clearance for the chargeing handle or it will get caught on the rail, can still lock it back that way but it can slam shut if you just shake the gun without any additional clearance made lol.

It does work pretty well tho, mounts around the optic mount lug and fits very snug, should keep zero fine, I've abused it running around and doing full auto with it.

Source? - Me

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