Images of rifle

[Roscoe Snyder]

Assume it's 5.56 (that's what the barrel says, right?), which means you can shoot anything you like, 5.56 or .223. You can also shoot 55 gr. or 62 gr. bullets in it.

I don't really know how critical the .223/5.56 distinction is in AR-15 type rifles is, but then I haven't fooled around with stainless-barrelled NM type guns and the like anyway. What I have heard in times gone by was that it was dangerous to shoot 5.56 in bolt action rifles chambered for .223 and that sometimes they would blow up.

[jmoore]

.223 Rem chambers have a shorter throat than the 5,56. But all ".223" Colts are chambered in 5,56 spec. no matter what's on the receiver (unless, of course, it says .222 Rem!)

I sold a bunch of these Colts whilst working my way through school, and Roscoe Snyder's info is spot on.

I like these early rifles for their "Government profile",1-7 twist, Chrome lined, bayonet lugged barrels.

[DaveN]

My friend said if the barrel is marked 5.56 you can shoot both 5.56 and .223 but if it is marked .223 do not shoot 5.56 in it. Is 5.56 a hotter round? My barrel is marked 5.56 on the barrel and both 5.56 and .223 on the receiver of my Olympic Arms so I'm good for both.
My thought was.... Isn't 7.62 x ?? NATO a .308 sort of 6 of 1 and a half a dozen of another but in the end all the same? Just wondering?

[Bill Hollinger]

If wikipedia can be trusted:

.223:
Case type Rimless, bottleneck
Bullet diameter .224 in (5.7 mm)
Neck diameter .253 in (6.4 mm)
Shoulder diameter .354 in (9.0 mm)
Base diameter .376 in (9.6 mm)
Rim diameter .378 in (9.6 mm)
Rim thickness .045 in (1.1 mm)
Case length 1.76 in (45 mm)
Overall length 2.26 in (57 mm)
Rifling twist 1 in 12 inch (military style rifles use 1:7 to 1:10 to stabilize heavier bullets)
Primer type Small rifle
Maximum pressure 55,000 psi (380 MPa)

5.56 X 45mm:
Case type Rimless, bottleneck
Bullet diameter 5.70 mm (0.224 in)
Neck diameter 6.43 mm (0.253 in)
Shoulder diameter 9.00 mm (0.354 in)
Base diameter 9.58 mm (0.377 in)
Rim diameter 9.60 mm (0.378 in)
Rim thickness 1.14 mm (0.045 in)
Case length 44.70 mm (1.760 in)
Overall length 57.40 mm (2.260 in)
Case capacity 1.85 cm³ (29 gr H2O)
Rifling twist 178 mm or 229 mm (1 in 7 in or 9 in, originally 1 in 14 in)
Primer type Small rifle
Maximum pressure 430.00 MPa (62,366 psi)

[LeagleEagle]

Just about all the ammo for AR-15s is 5.56mm Nato, e.g., M855