Compare 6.5 Grendel, .350 Legend, .308 Win, and more for deer hunting on AR platforms. This guide breaks the topic down in plain language so you can make a confident decision for your build.
Picking a deer caliber for an AR comes down to your terrain, your shot distances, and your state's regulations. A 50-yard shot in a cedar thicket and a 300-yard cross on an open food plot are two different problems, and the right cartridge for one is the wrong one for the other.
What Makes a Caliber Legal and Ethical
Most states that regulate rifle calibers for deer require a minimum .243 bullet diameter and roughly 1,000 ft-lbs of energy at 100 yards. Illinois, Iowa, Indiana, Ohio, and Michigan all set that .243 floor to ensure adequate terminal performance on whitetail-sized game.
That 1,000 ft-lb threshold is exactly why .300 Blackout is considered marginal for deer even where it is legal. A 125-grain supersonic load makes roughly 1,100 to 1,200 ft-lbs at the muzzle and bleeds energy fast. By 150 yards you are pushing the ethical edge on a mature buck.
Texas, Oklahoma, and Kansas impose no minimum diameter or energy floor. Any centerfire rifle caliber is legal for deer, which opens the whole menu.
The Straight-Wall Question
A straight-wall cartridge is defined by geometry: case taper under 5 degrees from base to mouth. The 350 Legend qualifies. The 450 Bushmaster qualifies. The 6.5 Grendel does not, because its case is bottlenecked. That matters in states like Ohio and Indiana that opened previously shotgun-only zones to straight-wall cartridges only.
That regulatory change is why 350 Legend adoption climbed sharply after its 2019 introduction. If you hunt a restricted zone, your caliber decision is partly made for you. If you do not, range and terrain decide it.
The Top AR-15 Deer Calibers Compared
350 Legend pushes a 150-grain bullet at 2,300 fps for 1,762 ft-lbs. Effective on whitetail to 200 yards with mild recoil, which makes it a solid pick for youth hunters and anyone new to the platform. It is also the only cartridge here legal in Midwest straight-wall-only states. Magazine capacity drops compared to 5.56 because of the larger case diameter. Our 350 Legend upper guide covers the build.
6.5 Grendel is the best AR-15 deer caliber at distance. A 123-grain bullet leaves at 2,580 fps with 1,818 ft-lbs, and the 123-grain Hornady ELD-M carries a 0.506 BC, which produces less drop at 300 and 400 yards than anything else in this comparison. It needs a dedicated bolt and barrel on a standard AR-15 lower. See whether the Grendel fits your hunt.
6.8 SPC II runs a 110-grain bullet around 2,570 fps for roughly 1,613 ft-lbs. The larger .277 frontal diameter delivers hard terminal performance inside 250 yards, which suits close timber work. It gives up energy retention to the Grendel past 300 yards.
Big-Bore Options When You Want More Punch
450 Bushmaster pushes a 250-grain bullet at roughly 2,200 fps for around 2,686 ft-lbs at the muzzle. That is serious energy on an AR-15 frame, effective on deer and hogs to about 250 yards, and legal in every Midwest straight-wall state. Be honest about the recoil: it hits roughly like a .30-06 in a light rifle. Magazine capacity typically runs five to seven rounds. Our big-bore comparison covers the alternatives.
338 ARC runs a 185-grain bullet at 2,750 fps and stays effective past 500 yards on an AR-15 lower. It is not a straight-wall cartridge, so it is built for states where all centerfire calibers are legal. If your shots stretch past 400 yards across open ground, this is the one to look at. Start with 338 ARC for hunting.
Pick the cartridge that matches your longest realistic shot, then verify it still hits hard enough at your shortest.
AR-10 Calibers: .243 and .308
The .243 Winchester is a flat-shooting deer cartridge with light recoil that reaches well past 300 yards. The .308 Winchester is the most available and most proven, with heavy bonded bullets for large hogs and bad angles.
Both require an AR-10 or LR-308 pattern platform. Nothing from an AR-15 carries over, and the complete rifle runs 1.5 to 2.5 pounds heavier. See our AR-15 vs AR-10 breakdown before you commit, and 6.5 Creedmoor vs .308 if you are choosing between large-frame chamberings.
Matching Caliber to Your Hunting Conditions
Inside 200 yards, nearly any cartridge on this list gets it done. Beyond 200, ballistic coefficient and retained energy start separating the good choices from the wrong ones.
- Under 150 yards (timber, creek bottoms, thick brush): 350 Legend, 450 Bushmaster, and 6.8 SPC II. Big frontal diameter and hard terminal impact.
- 150 to 300 yards and beyond (open pasture, food plots): 6.5 Grendel, 338 ARC, .243 Win, and .308 Win hold velocity and energy where it counts.
Barrel length and twist rate matter as much as the headstamp. Our barrel length guide and twist rate guide cover how to spec each build so the load you actually shoot stabilizes properly.
Regulations change, so verify current rules with your state wildlife agency before ordering a new upper, and check refuge-specific rules separately when you hunt federal ground.
Browse complete AR uppers or contact the shop at ar15parts.com to talk through which caliber fits your terrain before you buy.
