So it turns out this is not as simple as it seems.  

I happened upon an "optic ready" M&P Shield Plus the other day.  Purchased it and ordered a 507k.  

That's where things got tricky.  The Shield Plus is cut for Shield RMSc footprint, which-it turns out-isn't directly compatible with the 507k.

The cutout is the right size, but it includes four nubs that stick up at the corners to help hold the optic in place.  Generally speaking, this is a good thing.  Unfortunately, the 507k only has cutouts for nubs at the front corners, not the back.  

So I head over to my buddy's house (he has a milling machine) and have him mill the rear nubs flush.  A little spray-paint to cover the surface where the nubs used to be and we should be good-to-go.  

But no.  The front nubs are too tall so the optic won't sit flat.  So I break out the file and carefully start removing material (getting through the surface coating isn't easy--that stuff is tough!).

Anyway, after some filing they become short enough, but the optic still won't sit flush--I can just see daylight between the optic and the slide.  I pull out the calipers and the nub appears to be just slightly flared at the bottom.  

So out comes the tube of RTV and I make a gasket around the cutout.  I sit the optic on there and it looks great!

Then I try the screws that came with the 507k.  There are two sizes, neither was the right one.  

So a trip to home depot later, I had stainless steel screws that fit (#6 - 32 x 1/2 inch).  Philips head, but they fit.  They are also silver, but a little Birchwood Casey Super Black touch up paint and all was well.

Was it worth it?  I think so--the factory night sights are visible through the optic (probably wouldn't be with an adaptor plate) and the overall ascetics are pleasing to me.  

And here's the finished product (I should have taken pictures along the way, but I didn't know this was going to be such an ordeal).

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Sounds identical to the process of getting a Hellcat mounted with one.

Remove two lugs, shorten the other two about 10-15 mils.

Congrats, you'll be very happy with it!

i did a similar custom job on an m&p 2.0 core. it doesn't come with holosun 407k adaptors so i just sanded off the back lugs on one of the adaptors meant for the trijicon i think where the front lugs fit to have it seat snugly, then i used a longer screw meant for another optic and secured it with loctite

Same with a 43x MOS.  I bought a plate.  If the shield plus had dropped with an optic cut id have never bothered with the 43x.

Not gonna lie, if I had known it was going to be this big of a pain in the ass to mount my 407k to the Shield Plus, I would have kept my 365XL.

Thanks for sharing this info. This is basically what I gathered from my research and is why I’m shopping for a non OR model and plan to get it cut for the 507k.

Considering the popularity of Holosun, it’s really quite self-centered of S&W to use this type of cut.

Actually, Holosun's the one at fault, since they're the ones who neglected the RMS/RMSc standard.

Pocket conversion $29

Thank you for this. I just got a Shield Plus OR myself.

Now that’s very cool! Thanks for sharing. That opens up options to inexpensively convert a pistol to the backward compatible Holosun K pattern.

RMSc may be the micro pistol standard but Holosun K has a large portion of the market and their footprint is compatible with RMSc optics. So why not use the Holosun K cut on micro pistols to allow people the choice of RMSc or K optics? Using the RMSc cut means customers can’t use a K optic without modifications. It doesn’t make much sense to me.

They did great work on my Shield+

I'll use them again.