The video opens with live fire using a CMMG 5.7x28 conversion upper mounted on a Radical Firearms AR pistol lower originally set up for .300 Blackout. The host chambers the rifle, notes appreciation for the oversized charging handle, and sends several rounds downrange. The 5.7x28 is described as offering noticeable velocity with very low recoil, sitting between .22 LR and 5.56/.223 in felt impulse. The round is referenced alongside platforms that popularized it, including the FN PS90, FN Five-seveN, and Ruger-57 pistol. Initial shooting impressions emphasize how controllable and enjoyable the 5.7x28 upper is on a standard AR-15 lower.
The CMMG Mk57 upper is shown with its dedicated 5.7x28 magazines. The kit includes three 40-round CMMG 5.7 magazines that resemble AR magazines but are sized for the 5.7 cartridge. The host highlights the generous capacity and notes CMMG’s broader lineup, including the Mutant series, other 5.7 firearms, and a .22 LR conversion kit. The upper features a threaded 5 to 5.5 inch barrel, a full-length Picatinny rail for optics, and M-LOK attachment slots around the handguard. A SIG MSR red dot is mounted as a general-purpose range optic. The rifle locks back on empty, and the Radical Firearms lower with an MFT (Mission First Tactical) grip is noted as comfortable and compatible with the Mk57 upper and 5.7 magazines.
The host switches to a Daniel Defense Mk18 equipped with a Fostech Echo trigger to test the Mk57 upper in a different configuration. Multiple rapid strings and mag dumps are fired in Echo mode, demonstrating how quickly a 40-round 5.7x28 magazine can be emptied. Recoil and muzzle rise appear minimal, and the host focuses on watching the muzzle to observe how little it moves under rapid fire. The Echo trigger is explained: it fires once on the pull and once on the release, and remains legal and safe when used correctly. A safety demonstration shows that if a shot is fired in Echo mode, the shooter can switch the selector back to semi while holding the trigger to prevent the second shot; releasing the trigger then produces a normal semi-auto reset.
The Mk57 upper is run on the Daniel Defense Mk18 SBR lower with the Fostech Echo trigger, emphasizing how the 5.7x28 setup performs on a registered SBR with a full stock and the option for a vertical grip. The combination of the Echo trigger, short 5-inch barrel, and 5.7x28 chambering is described as very controllable with extremely low recoil. The host notes that even when the upper is used on a pistol lower with only a buffer tube and no stock, the firearm remains comfortable and easy to manage. The oversized ambidextrous charging handle is again highlighted as a practical feature that makes manipulation easier from either side. Overall, the Mk57 upper is shown to run reliably and smoothly on both pistol and SBR lowers.
With the upper removed from the lower, the host provides a closer look at the CMMG Banshee Mk57 5.7x28 complete upper. It ships optics-ready, without an included optic, but comes with three 40-round magazines. The upper uses a 7075 aluminum receiver and a 5-inch barrel with a 1:9 twist rate. The barrel has a 1/2x28 thread pitch and a thread protector, allowing use of common AR-15 muzzle devices and compatible suppressors. A full-length Picatinny rail runs along the top for mounting optics such as the SIG MSR red dot shown. The handguard features M-LOK slots around the rail for accessories. CMMG’s oversized ambidextrous charging handle is demonstrated and compared to a “batwing” style, and the upper includes a forward assist similar to many modern AR-15 uppers. The unit is presented as a standard AR-pattern upper configured specifically for 5.7x28.
The 5.7x28 cartridge is shown and described as a fast, lightweight round, with the host estimating velocity around 2,800 feet per second and inviting viewers to confirm exact figures. The 5.7x28 is visually compared to 5.56 and .308 Winchester, appearing like a scaled-down 5.56, and later contrasted with a .50 BMG round to illustrate size differences. The host notes that the Mk57 upper offers a way to run 5.7x28 on an existing AR-15 lower for those who may find an FN PS90 cost-prohibitive, or who already own pistols like the Ruger-57 or FN Five-seveN and want a matching AR platform. CMMG also produces complete Banshee firearms in 5.7x28, and the Mk57 upper is shown to function well with the Fostech Echo trigger. The video closes by directing viewers to ClassicFirearms.com for more information and related giveaways.
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