OPF is a family of adapter plates for mounting mini red dot sights on auto loading pistols.
OPF-G, RMR (Optics Platform, Glock, Forward Controls, for RMR) is a Glock MOS Adapter Set 01 compatible RMR/SRO interface plate. It is a collaboration between Tom Shields, the former head coach of USMC's shooting team and Forward Controls.
Tom had set out a list of objectives, which set the foundation and eventual shape of OPF-G, RMR, it's another example of function over form, and form follows function.
1. Machined in steel
2. Front and rear fences/lugs
3. Correct screw length, screws to be Torx
2. Front and rear fences/lugs
3. Correct screw length, screws to be Torx
4. Maintain Glock MOS plate thickness
5. Inclusion of VC-3
An often asked question is why we decided to use steel. The reasons are:
1. Glock's MOS plate is steel, we see no reason to change it.
2. Sight to plate, and plate to sight screws are steel, we prefer steel for this application.
3. We do not deem aluminum, 6061 or 7075, suitable this application.
For our AR15/M16 components, we have an H designation (for heavy), such as ESF-H, EMR-H, and MSQ-H. We don't sacrifice durability for light weight, it's been our practice for years. It is our opinion while aluminum might appear adequate for the job at first glance, it's eliminated as a suitable material for OPF from the outset for a single reason: we want steel screws to go in steel screw holes for OPF. We can probably steel line a aluminum plate's screw holes, but it'd be simpler to make OPF in steel to begin with. We like to minimize parts counts whenever possible.
Glock's MOS plate thickness allows for sufficient thread engagement, no more, and no less. OPF-G, RMR doesn't require a sealer plate, as it provides full width RMR support, we gain a bit more thread engagement by simply eliminating the need for a sealer plate. We looked at increasing the OPF's thickness to gain more thread engagement, and quickly realized that in exchange for 1/4 to 1/2 turn of thread engagement, we'd give up a few things in the process: parts availability (a thicker plate would require longer, custom screws), iron sights would no longer be compatible, and hold over would change, which would require users to retrain, and it may render many holsters designed for Glock MOS incompatible. Trading a minor, almost imperceptible improvement for a host of not inconsequential issues isn't our idea of problem solving.
OPF-G, RMR's front and rear recoil fences/lugs are designed to snugly cradle the sight in between. The design replicates the effect of a milled slide, wherein the sight is neatly sandwiched between barriers and unable to move along the bore. The design also quite effectively limits the sight from rotating on the OPF-G, RMR. In addition to the side by side recoil lugs for the RMR, the front and rear recoil fences/lugs prevent the sight from twisting on the plate.
The tight fit of an RMR and our plate prompted the range master/armorer of a large agency to compare it to the Dairy Queen Blizzard test, where an RMR is sat on the OPF-G, RMR and placed upside down, without the sight to plate screws. Note that not all the RMR and OPF-G, RMR combinations will do this due to tolerances of RMRs and OPF-G, RMR), this isn't a test. Even if the sight can't stay on the plate upside down without screws, the front and rear recoil fences/lugs perform what they're designed to do.
We designed the fit to be as precise as we could, given our own tolerances, and tolerances of the Glock slide and Trijicon RMR. While it's impossible to always have a perfect fit with a 0.001 or 0.002 gap, and this gap will vary, the presence of a gap between the sight and plate, as well as plate and slide is unavoidable. Often this gap is impossible to see, except on close up pictures.
OPF-G, RMR has minimal aesthetics. We laser engrave a small Cygnus logo, and the words "RMR/SRO ONLY", as we do not support OPF-G, RMR with Holosun sights. The precision fit nature of the design doesn't allow most Holosun sights to be installed within the front and rear recoil fences/lugs.
We do not engrave the screw sizes and thread pitch values on the plate. Though the screws are easy to distinguish for those that handle firearms on a regular basis, we don't think most users can tell the thread pitch and size values by simply looking at the screws. Instead, the screws are packed in small bags with labels, with easy to follow instructions on the product card. Attention to detail matters in its application.
Some might notice a very slight gap in the plate's rear and slide.
The slight plate to slide gap isn't an issue, and it's unavoidable.
Of about 30 MOS cut slides samples measured:
The smallest pocket was 1.930 measured on the outside corners of both sides of the cut.
The largest was 1.9315
The most common measurement was 1.931, being 17 of 22. 1.9315 was one Gen4 slide. 1.930 was measured 4 times, on 2 Gen5 and 2 Gen4 slides.
While the gap is too small to slide a human hair in on some slides, some are slightly larger, we're talking 0.0015. We were debating whether we should try to eliminate the gap, doing so will invariably guarantee that for others, the plate will have to be fitted.
We hold pretty good tolerances on ours, but this isn't enough, for Glock holds a tolerance as well. If we made ours 1.931, folks with 1.90 length MOS plate slide cut will have to fit their plate. If we made it 1.9315, everyone shorter than that length will have to fit their plate. Ours is 1.930. and it fits all varying lengths.
We can't make ours in 1.930, 1.931, and 1.9315 increments. The issue more important and pertinent to us is sight too plate fit.
Of about 30 MOS cut slides samples measured:
The smallest pocket was 1.930 measured on the outside corners of both sides of the cut.
The largest was 1.9315
The most common measurement was 1.931, being 17 of 22. 1.9315 was one Gen4 slide. 1.930 was measured 4 times, on 2 Gen5 and 2 Gen4 slides.
While the gap is too small to slide a human hair in on some slides, some are slightly larger, we're talking 0.0015. We were debating whether we should try to eliminate the gap, doing so will invariably guarantee that for others, the plate will have to be fitted.
We hold pretty good tolerances on ours, but this isn't enough, for Glock holds a tolerance as well. If we made ours 1.931, folks with 1.90 length MOS plate slide cut will have to fit their plate. If we made it 1.9315, everyone shorter than that length will have to fit their plate. Ours is 1.930. and it fits all varying lengths.
We can't make ours in 1.930, 1.931, and 1.9315 increments. The issue more important and pertinent to us is sight too plate fit.
A few words from our friend Gary W Thomas II, AIA, NCARB in engineering terms:
To understand the concerns with the Glock OEM MOS plate an explanation of the loads imparted upon the fasteners is required. When the handgun is fired, the recoil generates a lateral load in the direction of the slide's movement. This load is transferred through to the fasteners connecting the plate and optic. The Glock OEM plate does not maintain the optic in statis thereby imparting dynamic lateral loads upon the fasteners at the fastener shear plane. These loads cannot be resisted by the fasteners indefinitely and may result in mounting failure wherein the fastener shears at the shear plane.
Forward Controls Design's solution is to maintain the optic in a static position relative to the lateral load path by adding fore and aft recoil lugs about the optic. The front lug resists the dynamic load imparted by the slide inertia during the slide's rearward travel (ejection cycle) while the rear lug resists the dynamic load imparted by the slide inertia during the slide's forward travel (feed cycle). Therefore, OPF-G, RMR maintains the optic in a static position relative to the fasteners and thereby effectively reduces (if not deletes) the dynamic lateral load imparted upon the fasteners at the fastener shear plane.
Forward Controls Design's solution is to maintain the optic in a static position relative to the lateral load path by adding fore and aft recoil lugs about the optic. The front lug resists the dynamic load imparted by the slide inertia during the slide's rearward travel (ejection cycle) while the rear lug resists the dynamic load imparted by the slide inertia during the slide's forward travel (feed cycle). Therefore, OPF-G, RMR maintains the optic in a static position relative to the fasteners and thereby effectively reduces (if not deletes) the dynamic lateral load imparted upon the fasteners at the fastener shear plane.