90.72
Yes.
It will go bang and exit the gun at the muzzle end.
By the manufacturer's headstamp (usually "LC" or "ADCOM") and the presence of the NATO headstamp (vs. the older M193, which did not have this).Additionally, there will be a green coloured ring around the projectile (although this may sometimes wear off over time).
M193 - BallM196 - TraceM199 - DummyM200 - Blank (Violet tip and 7 petal rose crimp)M855 - Ball (Green Tip)M856 - Tracer (Red Tip)M862 - Short Range Training Ammunition (Plastic with a Blue Tip)
It fires the 5.56x45mm cartridge. It is compatible with the 62 grain M855/SS109 ball, the 64 grain M856 tracer, blank cartridges, and it can use the 77 grain Mk. 262 cartridge. The slow twist of rifling (1 in 7) makes it impractical for use with the older 55 grain M193 ball ammo and 45 - 55 grain commercial .223 Remington loads.
The original M16 had a 20 inch barrel, whereas the M4 has a 14.5 inch barrel. The longer barrel of the M16 gave the round a higher velocity than the short barrel of the M4 does. However, according to military specs, the maximum effective range of the M4 against a point target is only 50 meters less than that of the M16, and the maximum effective range against an area target is unchanged. And I've just noticed you said M193 ammunition, and not SS109/M855. It should also be noted that the M16A1 and XM177 had a 1 in 12 inch twist rate, designed to stabilise the lighter 55 grain M193 cartridge, whereas the M16A2, M16A4, and M4 carbine have a 1 in 7 inch twist rate. Part of the reason for this change is rifling was to better stabilise the 62 grain SS109/M855 cartridge, although the specific twist was chosen for its ability to stabilise the 64 grain M856 cartridge, and can also be used with the 77 grain Mk 262 special ball cartridge. However, 1 in 7 is a bit fast of a rifling twist for the lightweight M193 cartridge. Although you can fire the M193 through a 1:7 barrel, the fast twist of rifling causes excessive spin with the lighter cartridge, which have the overall effect of reducing the round's stability and altering the terminal ballistics.
The original 55 grain M193 cartridge was, yes. It was a further development of an existing cartridge - the .223 Remington, itself derived from the .222 Remington.
That depends on which 5.56 round you had in mind. The original M193 cartridge used a 55 grain projectile. The current M855 and SS109 NATO standard cartridges use a 62 grain projectile. The M196 tracer (which complimented the M193 ball cartridge) uses a 54 grain projectile. The M202 cartridge used a 58 grain projectile. The experimental XM287 and XM288 cartridges used a 68 grain projectile. The M856 tracer (which compliments the M855/SS109) uses a 64 grain projectile. The M995 armour piercing cartridge uses a 52 grain projectile. The Mk. 262 Mod. 0/1 cartridge uses a 77 grain projectile.
Typically, the 5.56x45 62 grain NATO SS109 and M855. It can also fire the 77 grain Mk 262 cartridge. Civilian "M4geries" typically have a 1 in 9 pitch (vs. the 1 in 7 pitch of the mil spec rifles) which can accommodate lighter weight cartridges, such as the 55 grain 5.56x45 M193, and 45 to 55 grain .223 Remington.
.308 is identical in diameter to the 7.62x51 NATO cartridge (although the two are not exactly the same). .223 is identical in diameter to the 5.56x45 NATO (and M193) cartridge (though, again, they are not exactly the same). The .308 is larger.
That depends on what its chambered for.... Most AR-15's are chambered for the standard 5.56x45mm military round, although some will only have a .223 Remington chamber, and it not advisable to fire 5.56 rounds through these. There is also the .223 Wylde, which can handle all loadings of 5.56 and .223. Most commercial AR15 rifles will come with a 1:9 barrel twist rate, which can accommodate both the lightweight 45 and 55 grain commercial .223 and M193 cartridges, as well as the heavier 62 grain NATO cartridges. However, when you get into loads such as the 77 grain rounds, the 1:9 barrels won't stabilise them very well. 1:8 barrel twist is the most dynamic, and can handle anything from 55 grain .223 and M193 up to the 80 grain .223 Wylde, and everything in between. 1:7 twist is a bit too fast a rifling twist for the lightweight 45/55 grain .223 rounds and the 55 grain M193 rounds, and really is a bit excessive a twist rate for the 62 grain M855/SS109 (NATO standard) cartridges. But it's great for 75, 77, 80 grain projectiles.