Pistol optics can be confusing. And one of the more confusing things is understanding the Holosun K Series footprint vs the Shield RMSc footprint.
This article is going to make it crystal clear so keep reading.
We call the Holosun K Series footprint a "Modified RMSc footprint" because it's very similar with only a few differences.
The optics that have a Holosun K Series footprint are the 407K, 507K, EPS, and EPS Carry.
Holosun K Series Footprint vs Shield RMSc Footprint
- A normal Shield RMSc Footprint has 4 recoil lugs, two in the front, two in the rear
- The Holosun K Series footprint has two in the front only, none in the rear
- The Holosun K Series footprint also has shallower recoil lug recesses
Why is the Holosun K Series like this?
Because it's waterproof. In order for them to make it waterproof they had to eliminate the rear recoil lugs. The K Series is the only waterproof optic in this micro optic class.
How do you mount a Holosun K Series on your pistol?
1. Adapter plates
The unfortunate part about the Holosun K Series optics is that they don't have the rear recoil lugs. Most pistols that come with different plates usually have an RMSc plate, and pistols like the Glock 43X MOS and S&W M&P Shield Plus come with an RMSc cut slide.
The Holosun K series will not fit directly on these guns without an adapter like this one. This adapter essentially acts like a shim, eliminating the rear recoil lugs. The only downside is it adds some extra height to the optic.
2. Modifying your existing RMSc slide or optic plate
We don't recommend this unless you are a handy person but the other option is to file down your recoil lug tabs on your slide or optic plate.
As we mentioned above the only difference between the K Series and RMSc footprint is that the K series has shallower recoil lugs and they are only in the front.
Since everything else is the same, you can file down your rear recoil lugs to make them flush with the slide and you can file down the front lugs so they fit into the shallower lugs on the K series optic.
This really isn't that difficult to do, and do it at your own risk, but it is another option. Doing it this way would not add any extra height to the optic.
Here's a video showing how someone did it to their 43X MOS
Which pistols will the Holosun K Series fit directly on?
As we see more pistols get released, we are seeing more using the "K Series/Modified RMSc" footprint which is great.
As of right now these are the pistols we know will accept a Holosun K Series optic without any modification to the adapter plate or slide:
- Bul Armory SAS II Ultralight
- S&W M&P 5.7 (needs these screws)
- S&W Equalizer (needs these screws)
- Sig P322, 365X, 365XL, 365X-Macro, 365-380
- Canik TP9 Elite SC
- Mossberg 940 Tactical (Shotgun)
- Taurus TX22 Compact
- Taurus GX4, GX4 XL T.O.R.O
- Ruger Max-9
- Shadow Systems CR920
- PSA 5.7 Rock
- PSA Micro Dagger
- FN Reflex MRD
If you know of a pistol not on this list please reach out to us or leave a comment below letting us know.
Conclusion
When you get into the really small micro optics, the Holosun K has this little quirk to it. The easiest way to remember how to fit it is to get an adapter plate, see if your slide or plate has only two front recoil lug tabs, or attempt modifying your existing RMSc footprint to the K series.
We also think more guns in the future will choose to go the Holosun K Series footprint instead of the RMSc because RMSc optics can still fit on a Holosun K Series footprint, but the opposite is not true.
If you have any other questions reach our or leave a comment.
Thanks for reading.