What Is The Most Versatile AR-15?

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I was issued my first AR off a large armory rack in 1974. Like Heanry Ford’s Model T, the choices were limited. You could have anything you wanted so long as it came in black and was chambered in 5.56x45 NATO. That first AR was the M16A1. The primary differences from the original M16 were the forward assist and an improved flash hider. The AR world has changed. There are now countless options for nearly every component on an AR. Some choices, like finish and color, are personal preference, but many are purpose driven. I want a rail mount for sight options. Depending on what I’m doing, I might mount a big scope for shooting groups or varmints, a red dot for hogs, or a thermal for coyotes. For my purposes, I don’t much care if a stock folds, but adjustable length of pull is good as seasons change (and younger shooters grow), and an adjustable comb allows setting proper cheekweld as height of sight changes.

A New AR-15

I don’t often add lights or lasers to my ARs, so I don’t care much about additional rail strips here and there, but you might. M-LOK handguards are handy. There’s lots of ways to do it, but I want to securely mount a bipod forward-bottom on the handguard. Barrel length is mostly personal preference, depending on your purposes. I prefer longer barrels, purely because they wring out more velocity. For me, the standard 20-inch barrel is a good compromise between handiness and maintaining bullet speed and energy. When I use a suppressor, even a 20-inch barrel gets long and ungainly. If I shot my ARs suppressed all the time, especially if in vehicle-carry mode, I’d probably sacrifice velocity and go with an 18-inch barrel or possibly 16.

With barrels, we have a rifling twist dilemma as well as choice of length. This applies primarily to the several .22 centerfire AR cartridges, because .224 bullets come in such a huge weight range, commonly 40 to 90 grains. Today’s shift to longer, heavier, aerodynamic bullets means that, instead of taking appropriate twist for granted (as when I was young), we need to think about twist rate based on the bullets we are likely to shoot.

Gene Stoner’s original AR-15 started with a 1:14-inch twist, barely able to stabilize a 55-grain bullet. This quickly changed to 1:12. AR barrels with 1:14 twist are rare today, but I have an early bolt-action Kimber .223 with 1:14 twist that’s a tack-driver with light bullets and “minute of deer” accuracy with shorter (less aerodynamic) 60-grain bullets. Go heavier than that, and it’s done.

A favorite and much-used AR is one of the first Rock River southpaw guns in 5.56. I never thought about twist when I bought it, because heavy bullets were new … and .22 centerfires were still mostly illegal for deer. It has a 1:12 twist. When Kansas changed the regulations, I discovered that it shot OK with bullets up to 62 grains and was hopeless with anything heavier.

When the military went to the M16A4 (1997), they adopted a fast 1:7 twist that worked great with the then-new 62-grain NATO bullet as well as our heaviest current .224 bullets. If you do a lot of varmint hunting, this twist is too fast for consistent accuracy with 50-grain bullets.

Much more versatile are 1:9 and 1:8 twists, the former generally stabilizing bullets up to 75 grains, the latter up to 80 grains. However, you may still run into poor accuracy with light 40-grain bullets. If you have no need for extra-heavy bullets, 1:10 is also an option, fine for light varmint bullets and acceptable for deer-capable bullets into the high 60s. Because of the unusual weight range and variety of uses for ARs, makers often offer a choice of barrel twists, something you must think about.

CARTRIDGE CONFUSION

The .223/5.56 is the world’s most popular centerfire cartridge, so it has the greatest availability and variety of ammunition at the lowest prices. Although uncommon, AR uppers are available in .17 Remington, .204 Ruger, several .22 centerfires, and on up. My most frequent varmint hunting is prairie dogs. I’ve had a ball shooting them with larger AR cartridges: 6mm ARC, 6.5 Grendel, even .300 Blackout. For small varmints, all you need is accuracy, which any good AR in any chambering can deliver, and range.

Federal’s .224 Valkyrie, introduced in 2017, has more case capacity and is specified for 1:7 twist. Long-range shooters, both varmint hunters and competitors, love it because it uses the longest, heaviest, most aerodynamic .224 bullets at credible velocity. The newest cartridge is Hornady’s .22 ARC, based on the 6mm ARC (6.5 Grendel) case necked down. With amazing efficiency, it approaches .22-250 velocity from an AR. Like the Valkyrie, it is specified for 1:7 twist, with Hornady’s initial factory loads from 62 to 88 grains.

In .224, these are not “varmint bullet” weights. Heavy bullets kick more. That sounds like a moot point with .22 centerfires, but when shooting small varmints at distance, my preference is to use a cartridge and bullet with so little recoil that I can call shots through the scope and adjust. For the high-volume varmint shooting I do, I’m happy with the .204 Ruger or the good old 5.56 with bullets of 55 grains and less. They don’t have the range or wind-bucking ability of heavy .224 bullets, but with minimal recoil, I can call my shots through the scope.

UP TO DEER

The .17s and .20s aren’t adequate for game larger than coyotes. The .22 centerfires are adequate for whitetails and hogs, especially with heavier bullets designed for the purpose. One advantage to .22 centerfires is minimal recoil, so good shot placement is simplified. Even so, precise head or neck shots aren’t always possible, and few of us have the discipline to pass good heart/lung shots, especially if a big buck or extra-large boar comes along.

For body shots, I find the .22 centerfires adequate but marginal, regardless of bullet weight. Heavier .22 bullets designed for larger game (not match, target, or varmints) will penetrate, but the entrance wound is tiny. In my experience, through-and-through penetration isn’t common on larger deer and bigger hogs. If the bullet does pass through, the exit wound is also small. Therefore, body shots with .22 centerfires, even if perfectly placed, require more tracking. In our thick southeast Kansas timber, it’s tough, especially at sunset. So far, we haven’t lost a deer from a .22 centerfire, but we’ve had bad moments looking in the dark.

For deer and especially larger hogs, I prefer to step up. The 6mm ARC is a good place to start. It doesn’t lag far behind the .243 Winchester, no giant killer but a sound deer cartridge. Personally, I step up more.

After .223/5.56, .300 Blackout is the most popular AR cartridge. Fun to shoot, but I find it depressingly marginal as a hunting cartridge and have heard too many horror stories of failures in camps I’ve hunted in. If you use it, keep shots close and place them well. There’s no margin for error.

With more velocity, I think the 6mm ARC, 6.5 Grendel, 6.8 SPC, and 7.62x39 Russian are all better and more versatile hunting cartridges. Bill Wilson of Wilson Combat went through the hoops to get his .300 HAM’R SAAMI-approved. The HAM’R is a bigger hammer. With 125-grain bullets to 2,500 fps, it equals .30-30 energy, which is not damning with faint praise. If you like .30 caliber, HAM’R availability is growing, so keep your eye on this one.

IS BIGGER BETTER?

The challenge with the awesome AR platform is we’re restricted in both action and magazine box as to how much cartridge it can house. The words “AR Compatible” carry inherent limitations. By sacrificing magazine capacity and going to dedicated magazines and larger bolt faces, you can increase powder capacity with wider cases. You can then neck those cases up and down to change bullet diameter and weight, thus adjusting velocity, but there are limits.

Above .30 caliber, production choices include .338 ARC, .350 Legend, .400 Legend, .450 Bushmaster, .458 SOCOM, and .50 Beowulf from Alexander Arms. Hornady’s .338 ARC is brand new, and I love .33s. The supersonic load with 175-grain bullets at 2,075 fps beat the stuffing out of any .300 Blackout load. With a super-heavy 307-grain subsonic load, it also surpasses the Blackout for suppressed/subsonic use.

It’s not a giant-killer, but we need to understand there’s no such thing in an AR-15 action. The straight-wall .350 Legend certainly isn’t. Report and recoil are wonderfully mild, but despite its .35-caliber, it isn’t especially powerful. I rate it a close-range deer cartridge.

Winchester followed up last year with its big brother, the .400 Legend. AR-compatible and meeting all straight-wall criteria, the 215-grain bullet isn’t heavy for caliber but credibly zippy at 2,250 fps. I was impressed by its hitting power and consistent through-and-through penetration. My impression is it hits much harder than its little brother. Combining acceptable recoil with power, if I lived in a straight wall state or wanted a short-range thumper for deer and hogs, I’d look hard at the .400 Legend.

Then there’s the .450 Bushmaster, the most powerful of the factory AR cartridges. To fit the AR action, there are compromises in bullet weight and velocity. The Bushmaster’s most common 250-grain bullet clocks 2,200 fps, exceeding the energy of many .45-70 loads. It’s a thumper on both ends, awesome medicine for hogs and black bear. Keep ranges short and accept the recoil.

ALL-AROUND AR

There are no AR cartridges I’d willingly choose for Alaskan brown bear or Cape buffalo. I don’t see any ideal elk or moose cartridges in the mix, either, but if you keep ranges short, I’m confident many would do the job. For the stuff most of us hunt regularly, all that can be done with a 5.56 and the right bullets. But on larger deer and hogs, I want more gun.

Looking across the cartridge board, if you’re an occasional deer hunter mostly out for venison, the 6mm ARC has appeal. If, like me, you’re a serious deer hunter, rarely finding but always hoping for a huge buck, my choice is Bill Alexander’s 6.5 Grendel. Credible velocity coupled with 6.5mm bullet aerodynamics give it some reach, and I’ve seen how effective it is on big-bodied bucks.

Please study the accompanying chart. It took me frustrating hours to compile it. Though not all-
encompassing, it paints a picture. Long before the AR-15 existed, gunwriter, hunter, and career U.S. Army ordnance officer Colonel Townsend Whelen (1877-1961) theorized that 1,000 ft-lbs of energy at the animal was desirable for cleanly taking deer-sized game. We know this is not locked in stone, but it’s not a bad rule of thumb and worth considering. Keep your shots close, and there are many options.

To 300 yards, only the fastest .22s, 6mm ARC, and 6.5 Grendel deliver that level of energy. Along with adequate energy (whatever that is), I believe in bullet frontal area to transfer that energy quickly, deal a heavy blow, and create a larger wound channel. Compromises are essential. For all-around use, from personal defense to targets, varmints, and deer and hogs at medium distances, it’s hard to imagine a better compromise than an accurate, well-scoped 6.5 Grendel. This is as versatile as an AR-15 can be.

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