Banned for asking more questions.
There's a pretty big difference in form and less so in function, but it's still there and very important from an engineering standpoint. Feel free to look at the below pictures anytime you feel the need and youtube.com has a few WWII technical videos if you look up how they work. The receiver is built different to allow each one to function within its given capacity.
Given that the M1 Garand fires a 30.06 round and the M1 Carbine fires a .30 carbine round (same width, but shorter casing and flat nose), the receivers are proportioned appropriately. The carbine round will not go as far, so the carbine is also shortened to an assault rifle length for portability. This assists in fields such as the Pacific, where paratroopers and close quarters are more common. The 30.06 round will penetrate armor or several walls/people. The .30 carbine round will not penetrate, but provides a great deal of knock-back power.
The M1 Garand has the en bloc inserted from the top (en blocs have no moving parts), pushing the bullet guide down and allowing the bolt to push the first bullet into place. When fired, the bullet is pushed forward by the gas (as is true with any bullet) but just before the bullet leaves the barrel, the gas passes a small hole which leads into the gas cylinder (cylinder under the nose of the barrel). As the gas fills the cylinder, it pushes on the operating rod, which extends all the way from the gas cylinder to receiver (it is a cylinder shape inside the gas cylinder, but twists and turns into a square shape, ending with the handle you can see at the back end of the top, rear handguard). This pushes the bolt back to prime it for the next shot and puts pressure on the follower, advancing to the next round. The bullet leaves the barrel and the gas is relieved, allowing everything to snap forward into place. As you can imagine, this process is extremely fast. Keep in mind this is a simplification of the matter.
The M1 Carbine can not use the same method, because the short action and excessive gases would produce so much pressure that the gun would explode. To get around this, the gas trap from the M1 was redesigned by David Williams. The magazine would be loaded, the spring in the magazine allowing the gun to hold more bullets and not need a machine operated follower. When the gun is cocked, it readies the bullet and bolt similar to the M1. When it is fired, gases expand all the same, but you'll notice no gas cylinder on the front end of the gun. Inside the stock are two important components: A short operating rod (the handle of which can be seen on the side of the gun above the magazine) and a small valve with a wide foot on the back side. The gas enters a thin opening, pressing on front of the valve. The valve pushes back and the foot kicks a large, cubic area that makes up the front of the operating rod. As the operating rod is kicked back, the valve comes to a close and no more gas enters, waiting for the bullet to leave before pressure is relieved. The operating rod pushes back, cycling to a new bullet (which is advanced by the spring in the magazine) and priming the bolt. The gas, unlike the M1 Garand, does not contact the operating rod directly and the operating rod does not push on a follower, thus not being directly responsible for the bullet's advancement.
There are differences in the trigger assembly, but not a great deal until the M2, a carbine with three components in the trigger housing redesigned to allow for automatic fire and a selector switch added. Although a few showed up in WWII and many more in Korea, the M1 Garand remained the mainstay and the M14 and M16 were more desirable as fully automatic weapons.
Do also keep in mind other technical differences:
M1 Garand
Weight: 9.5 - 11.6 lbs. (4.31 - 5.3 kg)
Length: 43.5 in. (1,104.9 mm)
Barrel Length: 24 in. (609.6 mm)
M1 Carbine
Weight: 5.2 lbs. (2.4 kg)
Length: 35.6 in. (900 mm)
Barrel Length: 18 in. (460 mm)
I have an M1 Carbine as well. When you fire it, you get to know the differences pretty well. I also have a Russian Mosin-Nagant, Finnish Mosin-Nagant, Yugoslavian M48A, 1895 Chileno Mauser, and 1895 Chileno Mauser Short. The other rifles I have are show only although I plan to add some of the before mentioned to that list.
On the far right is a .30 carbine round.
