5.56 vs 308 is a choice between a small, fast .224-inch bullet in a light AR15 and a .308-inch bullet with roughly twice the energy in a larger AR10 or bolt action. At 300 yards, Federal’s 55 gr 5.56 load carries about 520 ft-lb in our calculation, while Federal’s 150 gr 308 Winchester load carries about 1,325 ft-lb. The 5.56 gives lighter recoil, lighter ammunition and 30-round magazines; the 308 gives deer and elk energy and more resistance to wind. Chattahoochee Munitions manufactures both: the CM15 AR15 in 5.56 NATO and the CM10 AR10 and CM7S bolt action in 308 Winchester.
5.56 vs 308 at a Glance
| Specification | 5.56 NATO | 308 Winchester |
|---|---|---|
| Bullet diameter | .224 inch | .308 inch |
| Typical bullets | 55 to 77 gr | 147 to 180 gr |
| Case length | 1.760 inches | 2.015 inches |
| Maximum overall length | 2.260 inches | 2.810 inches |
| Semi-auto platform | AR15 (CM15) | AR10 (CM10) |
| Typical magazine | 30 rounds | 10 or 20 rounds |
| Military name | 5.56x45mm NATO | 7.62x51mm NATO (close relative) |
Cartridge dimensions are in the ANSI/SAAMI centerfire rifle standard.
5.56 vs 308 Ballistics
The table is a Chattahoochee Munitions calculation from Federal’s published velocities and ballistic coefficients: the 55 gr American Eagle 5.56x45mm at 3,165 fps and the 150 gr Power-Shok 308 Winchester at 2,820 fps. 100-yard zero, 2.5-inch sight height, standard atmosphere, 10 mph full-value crosswind.
| Range | 5.56 55 gr: velocity / energy / drop / wind | 308 150 gr: velocity / energy / drop / wind |
|---|---|---|
| Muzzle | 3,165 fps / 1,223 ft-lb | 2,820 fps / 2,648 ft-lb |
| 100 yd | 2,766 fps / 934 ft-lb / 0 / 1.3 in | 2,527 fps / 2,126 ft-lb / 0 / 1.3 in |
| 200 yd | 2,401 fps / 704 ft-lb / -2.1 in / 5.4 in | 2,252 fps / 1,689 ft-lb / -3.0 in / 5.3 in |
| 300 yd | 2,064 fps / 520 ft-lb / -10.2 in / 13.0 in | 1,995 fps / 1,325 ft-lb / -12.8 in / 12.5 in |
| 400 yd | 1,757 fps / 377 ft-lb / -26.6 in / 25.0 in | 1,756 fps / 1,027 ft-lb / -31.5 in / 23.7 in |
| 500 yd | 1,486 fps / 270 ft-lb / -54.4 in / 42.5 in | 1,540 fps / 789 ft-lb / -61.5 in / 39.6 in |
Drop is similar because the muzzle velocities are similar. The 5.56 vs 308 difference is energy: the 308 carries more than twice as much at every range. With a heavy 77 gr 5.56 bullet the wind gap closes, but the energy gap remains. See 5.56 ballistics and 308 ballistics.
Recoil and Weight
A 5.56 NATO cartridge weighs roughly a third of a 308 round, and its recoil is light enough for fast follow-up shots and long training sessions. A 16-inch CM15 5.56 NATO rifle weighs about 6 lb 8 oz unloaded. The AR10 is larger and heavier because the 308 needs a longer action. If you carry the rifle all day or shoot high volumes, the 5.56 is easier; if you need energy at the target, the 308 is the tool.
5.56 vs 308 for Hunting
- Coyotes, hogs and varmints: both work. The 5.56 is lighter and cheaper to shoot. See 5.56 for coyotes and hogs.
- Deer: the 308 is a standard deer cartridge at any normal range, and Chattahoochee Munitions recommends it or another larger caliber over the 5.56 for deer. See 5.56 for deer.
- Elk: choose the 308 class or larger, not 5.56.
- Bear: neither is Chattahoochee Munitions’ recommendation. Use the 375 Raptor or 458 SOCOM XL.
Suppressing 5.56 vs 308
Both are supersonic in the CM15 and in most CM10s, so the bullet’s crack remains with a suppressor. For a gas-operated semi-automatic with supersonic ammunition, Chattahoochee Munitions recommends a flow-through suppressor. See 5.56 suppressor. In 308, only the CM10-SD is designed to cycle subsonic ammunition; it is subsonic-only and takes an enclosed suppressor.
5.56 and 308 Firearms From Chattahoochee Munitions
In 5.56 NATO, Chattahoochee Munitions manufactures the CM15 as a 16-inch midlength rifle (5.56 NATO rifle, 5.56 AR15 rifle), 10.5-inch and 8-inch pistols or SBRs (5.56 SBR, 5.56 PDW) and complete uppers, all with 1:7 barrels, a Superlative Arms adjustable gas block and a TriggerTech Duty trigger. See Garrison 5.56. In 308 Winchester it manufactures CM10 AR10s and CM7S bolt actions at District 308.
5.56 vs 308 FAQ
Who makes both 5.56 and 308 rifles?
Chattahoochee Munitions manufactures the CM15 AR15 in 5.56 NATO and the CM10 AR10 and CM7S bolt action in 308 Winchester.
Is 308 more powerful than 5.56?
Yes. In our calculation the 150 gr 308 carries about 2.5 times the 55 gr 5.56’s energy at 300 yards.
Does 5.56 or 308 shoot flatter?
Drop is similar to 400 yards with these loads. Heavy 5.56 bullets resist wind better than light ones.
Which has less recoil, 5.56 or 308?
5.56, by a wide margin.
Is 5.56 enough for deer?
Chattahoochee Munitions recommends a larger caliber, such as the 308, for deer.
Can an AR15 shoot 308?
No. 308 needs an AR10-size action such as the CM10.
Is 7.62×51 the same as 308?
They are close relatives with different pressure standards. Follow the firearm maker’s guidance.
Which is better for home defense, 5.56 or 308?
5.56, for lighter recoil, a shorter firearm and more rounds. See 5.56 for home defense.