A Coyote’s Worst Nightmare: CMMG’s Endeavor 300 Mk4 in 22 Nosler

The CMMG Endeavor 300, chambered in 22 Nosler, sent a 53-grain Varmageddon bullet out of the barrel at 3,535 fps, significantly outrunning similar-weight 223. Rem and 224 Valkyrie loads.

For nearly two decades, Missouri-based CMMG has focused on building affordable, high-quality AR rifles. During that time, the firm has built a reputation for thinking outside the box and coming up with such innovative offerings as the Mk47 Mutant, built around the 7.62x39mm cartridge, and the Anvil, built around the 458 SOCOM round.

I have enjoyed testing and hunting with those rifles, among other CMMG models, so I didn’t hesitate when offered a chance to test a newer gun in a newer cartridge specialized for long-distance hunting. Before I get to that, a bit of explanation is in order. CMMG rebranded their entire line of guns a couple of years ago, with the Banshee line consisting of pistols and short barrel rifles. The Resolute line consists of rifles and carbines, while the Endeavor line is designed for long-range and precision-oriented shooters. Within each of these lines are models designated as 100, 200, or 300 series guns, with 100-series guns representing basic models and 300-series guns representing the top of the line. Models with an Mk4 designation indicate that the receiver is based off the traditional Mil-Spec AR 15 receiver, while those with an Mk3 designation indicate a gun based off an AR 10 receiver.

With factory 22 Nosler ammo offerings topping out with 85-grain bullets, the author views the Endeavor 300 in 22 Nosler primarily as a long-range varmint and predator rifle.

The rifle sent to me for testing, the Endeavor 300 Mk4, was chambered for a very interesting cartridge, the 22 Nosler. Introduced four years ago, the 22 Nosler was designed to dramatically boost the power of a 22-caliber centerfire cartridge while functioning reliably in an AR rifle. With an advertised velocity of 3,450 fps for the factory 53-grain Varmageddon load, it outruns the 55-grain 223 Rem by 210 fps and the 60-grain 224 Valkyrie, its closest competitor, by 150 fps. It’s only 350 fps slower than the screaming 22-250 Rem. 55-grain load, but that’s an apples-to-oranges comparison because the 22-250 is not designed to run in an AR. With light, flat-shooting bullets, the 22 Nosler is a coyote’s worst nightmare.

Its main limitation is the fact that it’s tied to rifle barrels with a 1:8 rate of twist and won’t stabilize heavier bullets as well as, say, the 224 Valkyrie pushing 90-grain bullets out of a barrel with a faster 1:7 rate of twist. Factory 22 Nosler offerings top out with 85-grain bullets. That’s why I would classify the Endeavor 300 rifle in 22 Nosler primarily as a long-range varmint and predator rifle rather than a long-range target gun. The 300 Endeavor will, however, function nicely in this role in other available chamberings, which include 224 Valkyrie, 6mm ARC, 6.5 Grendel, 6.5 Creedmoor, and 308 Win.

With its 24-inch barrel and Magpul PRS buttstock, the Endeavor 300 is purpose-built for long-range shooting and hunting.

Even at a glance, it’s obvious that the Endeavor 300 in 22 Nosler is designed to go long – and look good doing so. It sports a 24-inch fluted, 416 stainless steel barrel with a recessed target crown, as well as a Magpul PRS GEN3 stock. This stock, with its tool-less length of pull and cheekpiece height adjustments using aluminum detent knobs, is ideal for long-range varmint work. Even the substantial rubber butt-pad is adjustable for cant and height. The gun also wears a Magpul MOE pistol grip, which I like for its aggressive stippling and ridges that provide a sure grip in inclement weather.

The Endeavor 300’s fluted, 24-inch stainless barrel produced slightly higher velocities than specified with tested factory ammo.

The handguard as well as the upper and lower receivers, made of 7075-T6 Aluminum, have a Cerakote finish to protect against the elements. My test rifle came in an attractive burnt bronze color, but that’s just one of 10 color options ranging from “bazooka green” to “stormtrooper white.” The upper-to-lower receiver fit on my test gun was nicely tight, with just a slight amount of side-to-side play.

There are plenty of options for mounting optics and accessories on the CMMG RML15 M-Lok handguard. This handguard has seven slots at both the 3 o’clock and 9 o’clock positions, and eight slots at the 6 o’clock position. On top, you’ll find a full-length Picatinny rail.

The CMMG RML15 M-Lok handguard has no fewer than 22 M-Lok attachment points and a full-length Picatinny rail, providing plenty of options for attaching optics and accessories.

Controls on this rifle are well-chosen to allow for efficient operation under any field conditions. The gun is equipped with CMMG’s oversized, ambidextrous charging handle, which is easy to operate behind a mounted rifle scope. There’s a large, grooved paddle-style bolt release latch and an oversized CMMG ambidextrous safety. The forward assist and shell deflector are in the usual locations.

The magazine well is beveled for easier insertion of magazines, and the gun ships with a single 10-round magazine. It’s important to note that this magazine is designed to work specifically with 22 Nosler, 224 Valkyrie, and 6.8 SPC cartridges. An enlarged trigger guard will easily accommodate a gloved finger.

The Endeavor is designed to work efficiently under all field conditions with an enlarged, ambidextrous charging handle and oversized, ambidextrous safety.

Of course, any gun designed for accurate, long-range work has to have a decent trigger, and there are plenty of AR rifles designed for long-range use that fail to live up to their potential, out of the box, because the guns ship with lousy triggers installed. Happily, the Endeavor is not one of them. The rifle is equipped with a Geissele Automatics SSA 2-Stage trigger. It has a short amount of initial take-up, and then stacks and breaks cleanly. I measured the pull weight at a consistent 4 lb., 10 oz. That’s slightly heavier than I prefer, but the trigger breaks so crisply that I found it no handicap at all.

For range testing, I mounted a Leupold Mark 4 4-14x50mm scope on the gun using a rock-solid Burris P.E.P.R. mount. This setup has served me well for testing ARs at distance thanks to the scope’s sharp glass and manual parallax adjustment. The first order of business was to run the two loads I had available for testing over my Competitive Edge Dynamics M2 chronograph to see if the Nosler ammo lived up to factory velocity claims.

The rifle ships with a Geissele Automatics SSA 2-Stage trigger — a profound improvement over the triggers supplied with the majority of factory AR rifles.

It did – and then some. I was pleasantly surprised when I clocked the 53-grain FB Tipped Varmageddon round at 3,535 fps, which is 85 fps faster than the factory stated number. Nosler’s 85-grain RDF (Reduced Drag Factor) match load stepped out at 2,781 fps, which is 31 fps above the factory number. I believe those velocities are fully attributable to the rifle’s 24-inch barrel, which helps to squeeze maximum velocity out of ammo.

The rifle was no slouch in the accuracy department, either. The 53-grain Varmageddon round produced an average of 100-yard groups of 0.80 inches and a best group measuring 0.47 inches. I don’t know about you, but I’m more than a little happy anytime I can get an unmodified AR, straight from the factory, to shoot sub-MOA groups. When I find one that does so with a bullet moving this fast, I have a sudden urge to break out the predator calls or make tracks for the nearest prairie dog town.

In range testing, the rifle produced sub-MOA average groups at 100 yards with Nosler’s 53-grain Varmageddon load. This would be the author’s go-to load for varmints and predators.

The 85-grain load shot well – but not quite as well – as the lighter load.  It turned in average groups measuring 1.28 inches with a 0.52-inch best group. That’s still perfectly acceptable accuracy for most hunting purposes you would use the 22 Nosler for, but I would stick with the lighter load for long-range varmint and predator shooting. It’s not that there’s anything wrong with the heavier match bullet. The results speak primarily to the bullet-weight limitations of the 22 Nosler in rifles with a 1:8 rate of twist – hence the reason for factory offerings topping out with bullets weighing 85 grains.

Functionally, the gun ran like a champ, with nary a hiccup. Weighing in at 8.6 lbs. empty, I wouldn’t exactly consider the rifle to be a “walking varminter” with the full-up added weight of a scope, mount, and loaded magazine, but it will certainly get the job done in this role if you don’t mind toting a little extra weight. If you only walk short distances to predator stands or do a lot of stationary shooting at varmints, this rifle may be just your cup of tea, for some added weight can steady things up nicely for long-range shots, especially when the wind is blowing.

The Magpul PRS GEN3 stock adjusts easily for the length of pull and cheekpiece height for a custom fit to the shooter.

MSRP for the rifle is $1749.95. If that’s too steep a price, or you simply need a lighter and more basic gun, you can find CMMG models in 22 Nosler for considerably less money in the Endeavor 100 and 200 series. All CMMG guns come with a lifetime warranty against defects in materials and workmanship.

SPECIFICATIONS: CMMG Endeavor 300 Mk4 22 Nosler
Caliber: 22 Nosler
Action: Direct-impingement semi-auto
Barrel: 24-in. 1:8 twist, fluted stainless
Gas Port: Rifle Length
Receiver: 7075-T6 Aluminum
Hand Guard: CMMG RML15 M-Lok handguard
Finish: Cerakote
Charging Handle: CMMG Oversized Ambidextrous
Butt Stock: Magpul PRS
Trigger: Geissele Automatics SSA 2-Stage
Safety Selector: CMMG Ambidextrous
Magazine: 10-round (224 Valkyrie/22 Nosler/6.8SPC)
Weight: 8.6 lbs. empty





Nagel’s Gun Shop


Weighing 8.6 lbs. empty, the Endeavor 300 is no lightweight, but that weight can be helpful in steadying up for long shots, especially under windy conditions.
The gun is equipped with a Magpul MOE pistol grip, which provides a solid grip in inclement weather.

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