1) Is there a difference between RMR and MOS cuts? Yes, that's why a plate is needed for MOS. A RMR is more "universal" for other optics than the MOS, which needs a plate.
2) In general, will companies that mill slides do an MOS cut? Have to ask them, most don't offer that option
3) Does anything change with respect to the rear sight on a Gen 4 G19 if I get the slide milled? You can keep it or move it to the front of the cut.
4) Will I need to get my slide refinished after milling? Most places that do the milling also offer the refinish.

Ultimately, it depends on what optics you want to use on your slide. More optic companies offer RMR footprint than MOS footprint (Glock's compromise solution to being "optic ready").

Easier and cheapest solution is to buy a Gen3 optic ready slide that is pre RMR cut, and a gen3 recoil spring. What generation lower are you putting this on?

A gen3 complete upper assembly can work on gen4 lowers, and gen5 lowers with a gen5 backplate.

 

An RMR cut allows you to mount an RMR, Holosun 507c, or anything that fits the same pattern without intervening plates, although you can often get plates to go from RMR to whatever optic you have as well. An MOS cut is versatile but will require an adapter plate for any optic except the Holosun model specifically designed for it.

If you're getting a slide milled anyway, you're probably best off selecting your optic first, then getting the cut done for that specific optic.

Good options for slide cuts include ATEI, Jagerworks, and CHPWS. Lots of other good options, those are just the first several that came to mind.

No time to address the other questions at the moment.

 

To my knowledge, MOS is a proprietary Glock pattern. Glock offers various adapter plates that go from the MOS on the bottom to various patterns on the top.

I think the only reason you'd have a shop cut an MOS pattern (if they even offer it), is because you don't yet know which type of optic you want... or want to have options to change later. But consider that the requirement of an adapter plate with the MOS cut will necessarily raise the optic higher than a direct fit. Lower is better. Also, fewer interfaces (parts) is better.

The RMR cut, which I believe was developed by Trijicon, has been adapted by many optic manufacturers, including Holosun.

That said.. Holosun does make one particular model, the SCS-MOS, that fits the MOS pattern directly without an adapter. Pretty cool. Even the Glock slide rear serrations are continuous on the base of the SCS-MOS optic. Clever!

Figure out which optic you like or want... then have the cut made to fit that optic (without an adapter in between). That's my "take" on this.

 

With the US dollar devaluation; being hard up for getting the cut done, buy a dovetail slide from EGW mounts. I have no financial relation with company. Just want to spread another option. Most dovetail slides are $50 bucks. I guess slide cutting businesses will have to tighten their belt with this great Bidenomics situation. The Ukraine billions are staying here in the US. You don't see the ARMS industry employees going on strike. Lake City and Radford Ammo factories are running at full capacity. Send more planes to Poland and the Baltic states. The Biden MAFIA are running wild across the globe, Right?

 

I’ve had three guns milled from two companies and have been happy. Have a Gen 4 MOS as well.

I don’t notice any difference when shooting when people talk about the “height” of the optic. Presents just the same and shoot just as well with any of them.

If you want to stick with a Gen 4, I wouldn’t hesitate getting it milled for the optic you want.

 

You might be aware of this already but here's a one-stop solution.

10-Day Red Dot Optic / Slide Cut Combo | Best Glock Accessories | GlockStore.com

To get the most out of your red dot optic sight, you really want to mount it right to your slide. Visit glockstore.com today for the Red Dot Optic Cut and all your other custom Glock modifications

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How about just getting another slide already set up for your situation?

 

Thank you all for the education! I have a bit more to think about.

 

$50 for dovetail or $120 to mill. I’d go milled every time.

 

I traveled this road a while back as I wanted an optic on a Gen 4 G29. I’m a fan of Holosun and originally was going to get an RMR cut for a 507C but after looking around and asking a lot of questions, decided to go with an MOS cut and mount the Holosun SCS. So far it has been a great choice. I was able to keep my steel sights as the SCS mounts low enough to co-witness. If I choose to go with a different optic in the future, I have the MOS cut and can use plates if needed to match whatever I would get. I don’t see changing optics though unless I decide to go with a closed emitter in the future. I had my slide done by BattleWerx and have zero complaints with their milling, refinishing, cost or time to complete.

 

C&H Percision does amazing work, and have
thier own optics which are amazing, I am literally sitting at my house today waiting for my Glock 34 slide that I had them mill, refinish, and direct mount thier COMP green dot to arrive.

 

Wow, this thread was resurrected. I figure it's worth an update:

I found my unicorn! A guy on another forum was selling a 19.4 MOS with the Holosun I wanted already on it, and I persuaded him to part it out. I bought the slide; he sold the frame separately to someone else. I'm very happy as I now have two almost-identical G19s (19.4 MOS and 19.5 MOS).

Appreciate all the recommendations.