Currently, there are five types of mounts out there for pistol optic mounts (PMO): Dovetail, direct mill, OEM plates, aftermarket slides, or an aftermarket cut & mount system.
The first one we had was a dovetail mount, which replaces the rear sight in the dovetail. Of the slide-mounted systems, these have been around the longest. Initially, they are the least expensive way to put an optic on a pistol you already own. My first optic, an Insights MRDS on a 1911, was done like this in 2010. It puts the optic pretty high up. As a result, it can be challenging to acquire the dot on presentation. Currently, my Non-lethal training 
ammunition (UTM) pistol and the Gunsite pistols used for force on force training are set-up this way.
Acceptable offerings include Raven Concealment System’s BALOR mount and Dueck Defense’s red dot back-up sight.
Having your slide milled for directly mounting a specific optic was the best way to go in the early PMO days. There was a drawback in that you could only have that slide machined for that particular optic model. Your back-up sights could be positioned to the front or rear of the optic as well. With the Aimpoint Acro P1, this type of solution will get the optic as low on the slide as possible. This achieves a tight fit between the PMO and the slide, which may do away with movement from cycling. If you use an older pistol and have settled on a specific make and model of optic, this is a solid option. I have M&Ps and Glocks done like this, including my last duty pistol, an M & P with an Acro. You’ll need to find a competent machinist or gunsmith who truly understands how to do this.
Two I can recommend from experience are Mark Housel at L&M Precision and Doug Holloway at Atei.
A few years back, Glock and Smith & Wesson introduced pistols with the slides cut for factory mounting plates for various PMO models; respectively, these are the MOS and CORE models. These were their slides precut for optics. They use plates that mount between the slide and optic, which fit the various optics while still mounting to that slide. The manufacturers have continued to expand their plate offerings. Sig Sauer is now doing this as well.
At least two aftermarket entities, C&H Precision and Forward Controls Design, are producing their own plates. These offerings include polymer plates and one designed to protect the front of the optic.
The MOS and CORE are the least expensive and most common method for switching to a pistol mounted optic. I only recently picked up a G17 MOS, and I’ll be experimenting with the different aftermarket plates.
Several aftermarket manufacturers are making slides already cut for specific PMOs or a manufacturer’s proprietary mounting system. Examples of this are slides from Unity with their Atom mount cut and Faxon Firearms.
Finally, we see aftermarket designed mounting systems. These involve a proprietary cut to the slide and a manufacturer’s designed plate for each optic they support. Unity Tactical has two different versions of their Atom mount; Agency Arms has their “AOS” Agency Optics System; and, most recently, Chamber’s Custom developed, tested, fielded, and licensed a 1911/2011. Three of the Unity Tactical Atom mount slides have made their way to me over the years.
I’m looking forward to the second version making its way into service.
Regardless of which one you choose, follow the manufacturers’ directions on installing the optics and plates.
Next month, we will discuss the various optic designs.
