Your Browser is OutdatedHOLOSUN - HS507K-X2 compatible? — 2 Answers
If the 507k Gen 1 and the X2 share the same footprint, there's a good possibility it will fit. Be aware that due to their aluminum housing and its wider varying tolerances, it may require handfitting as our cut is extremely precise and intended to be snug. As for the screws, you will likely need to shorten the screws provided with the optic from HS or source smaller ones that are 6-32.
While the sight footprint fits, the screws that come with a Holosun 507K X2 are a different pitch and length. The screws that come with the GGP slide aren't long enough to pass through the base of the 507K X2 and interface with the slide. I've been unsuccessful in finding screws that will match so be cautious