Rock Slide USA RS2FS45-RMR 45ACP GEN3 Upper for Glock 21 BLACK Optic Ready
Rock Slide USA RS2FS45-RMR Stripped Slide, Glock 21 Gen 3, .45 ACP, Black, RMR Cut
So you want an aggressive, vent-cut .45 ACP slide with an RMR optic cut for your G21 Gen 3 build. This slide delivers that. The Rock Slide USA RS2FS45-RMR, a stripped slide for Glock 21 Gen 3 and Polymer80 PF45 frames. Black finish. Aggressive vent cuts in the front half. RMR optic cut standard. Made in USA. Lifetime warranty.
Rock Slide USA RS2FS45-RMR 45ACP GEN3 Upper for Glock 21 BLACK Optic Ready This is a stripped slide — not a complete assembly. First, you get the slide body with the RMR cut, vent cuts, and Cross Armory channel liner included. Next, you source and install your own barrel, recoil spring assembly, firing pin, extractor, sights, and other internals separately. Finally, the RS2’s aggressive front vent cuts shed weight and allow use of ported barrels if that’s your build direction.
Will this Rock Slide USA RS2FS45-RMR 45ACP GEN3 Upper for Glock 21 BLACK Optic Ready fit my Glock 21 Gen 3 frame?
Yes, and it also fits Polymer80 PF45 frames. So this slide is machined specifically for Glock 21 Gen 3 and PF45 .45 ACP frame dimensions. Also, it accepts standard Glock 21 internal parts, sights, and barrels you’re not sourcing proprietary internals. However, this is Gen 3 specifically. It does not fit Gen 4 or Gen 5 Glock 21 frames. Therefore, confirm your frame generation before ordering.
What does the RS2 vent cuts designation mean?
Rock Slide USA RS2FS45-RMR 45ACP GEN3 Upper for Glock 21 BLACK Optic Ready Aggressive front-half window cuts for weight reduction and ported barrel compatibility. So the RS1 is Rock Slide’s cleaner, duty-style slide without vent cuts — popular with law enforcement and everyday carry customers. Also, the RS2 adds those aggressive vent cuts in the front half, making it the choice for competition and target shooters who want a lighter slide or need clearance for a ported barrel. Therefore, choose RS1 for a cleaner duty look, RS2 for competition-oriented aesthetics and function.
What’s actually included with this slide?
The stripped slide body and a few extras. So you receive the slide itself with RMR optic cut pre-machined, 4 screws, 1 wrench, and a free premium Cross Armory channel liner. However, no barrel, recoil spring assembly, firing pin, extractor, springs, sights, or cover plate are included. Therefore, budget for a complete set of G21 internals and your choice of sights when planning this build.
What optics fit the RMR cut on this Rock Slide USA RS2FS45-RMR 45ACP GEN3 Upper for Glock 21 BLACK Optic Ready?
The Trijicon RMR and compatible footprint red dots. So the RMR cut is one of the most common pistol optic footprints in the industry. Also, Holosun’s 407C and 507C series, along with other RMR-compatible optics, mount directly to this cut. Therefore, you have a broad selection of optics available, not just Trijicon’s own lineup.
Who is this Rock Slide USA RS2FS45-RMR 45ACP GEN3 Upper for Glock 21 BLACK Optic Ready best for?
This Rock Slide USA RS2FS45-RMR 45ACP GEN3 Upper for Glock 21 BLACK Optic Ready fits G21 Gen 3 owners or PF45 builders who want a custom-look .45 ACP slide with optic capability, at a competitive price. So if you want the aggressive RS2 vent-cut look with an RMR mount ready to go, this slide covers that in one purchase. Also good for competition shooters running ported .45 ACP barrels who need front clearance.
Specs Table
| Spec | Detail |
|---|---|
| Compatibility | Glock 21 Gen 3, Polymer80 PF45 (.45 ACP frames) — NOT for Gen 4 or Gen 5 |
| Caliber | .45 ACP |
| Model | RS2FS45-RMR (RS2 = vent cuts, RMR = optic cut) |
| Configuration | Stripped slide (no internals, no sights, no barrel) |
| Optic Cut | RMR (Trijicon RMR footprint; also fits Holosun 407C/507C and other RMR-compatible optics) |
| Finish | Black |
| Vent Cuts | Yes aggressive front-half window cuts |
| Internals | Takes standard Glock 21 parts and barrels |
| Includes | Stripped slide, 4 screws, 1 wrench, Cross Armory premium channel liner |
| Not Included | Barrel, recoil spring, firing pin, extractor, sights, cover plate |
| Manufacturing | 100% Made in USA |
| Warranty | Lifetime warranty |
| Best For | Competition builds, PF45 custom builds, ported barrel setups, optic-ready .45 ACP |
| Weight | verify |
| Price | $220 |
FAQ
Is this a Rock Slide USA RS2FS45-RMR 45ACP GEN3 Upper for Glock 21 BLACK Optic Ready or a stripped slide? Stripped. This ships with the slide body, screws, wrench, and channel liner only. No barrel, internals, or sights are included.
Will this fit a Gen 4 Glock 21? No. This is Gen 3 specific. Gen 4 frames use a different slide interface.
What optics fit the RMR cut? Trijicon RMR, Holosun 407C, 507C, and other RMR-footprint compatible red dots.
Does this slide work with Polymer80 PF45 frames? Yes. Rock Slide USA confirms PF45 compatibility alongside Gen 3 Glock 21 frames.
What Glock 21 parts do I need to complete the build? Barrel, recoil spring assembly, firing pin assembly, extractor, springs, pins, sights, and a cover plate or your chosen optic.
What’s the difference between RS1 and RS2? RS1 is a clean, duty-style slide. RS2 adds aggressive front vent cuts for weight reduction and ported barrel compatibility.
What warranty comes with this slide? Rock Slide USA backs it with a lifetime warranty against manufacturing defects.
Find more Rock Slide USA slides and Glock 21 build parts at gunpartspalace.com.
