I've thought about writing on this subject for a while. In searching their history I found several good articles through out the net so I won't take too much time with that. Let's suffice it to say that everything started with John C. Garand and his celebrated M1 rifle. Post WWII there were requests for improvement. For the most part more ammunition capacity and a detachable magazine was wanted. The question was how to do it. Once again they turned to Mr. Garand. He gave them his initial drawings but in them the rifle was still chambered in .30-06 and that wasn't what was really wanted by the time said drawings arrived. You see, one of the other men on the project was working on a new ammunition based on the .30-06 but shorter, lighter (some what) but performed almost identically to the .30-06. Of course that was the 7.62x51 NATO or the .308 Win.
When examining the action there was very little that needed to be changed. The trigger guard needed to be opened up for the magazine and a retention system added. Not that difficult. Make the magazine rock into place so there is a place for it to be held front and rear. Little need be done to the receiver for that to happen. Minor changes in the original machining process and you have it.
We can always use a higher rate of fire in a battle rifle. That's a given. So we have the first major change in the rifle. On the exposed right locking lug they simply added a steel roller. Keep it lubed and it will serve you well. Since we took the metal to metal friction out of the picture on this side the action is much cycles faster.
There was a function on the M14 that doesn't exist on the civilian version. That is the selection knob. Sure you still had the same safety lever as the M1. The trigger mech still functioned the same as the M1. But now with the M14 on the back of the receiver we have a knob that by turning to one setting or the other one can choose between the M1's semi-auto and the new full auto. This effectively gave us the worlds only battle rifle that dueled as a squad automatic weapon. Of course for the civilian market this feature was never added.
These are fantastic rifles that just never quit. They're built tough as a tank. I've worked with ones that had seen action in Vietnam, therefore having the full auto knob, That still shot remarkably well. With a good shock bedding job these rifles are still used as sniper/ dedicated marksman rifles. They're great for shots up to 800 meters depending on the quality of the bedding job and the person behind the trigger. I've watched Marine Scout Snipers with these rifles make up to 1000 meter shots with these accurately. Of course at that range you are trying for minute of human not head shots.
There's enough room in the receivers of the M1, M14, M1A to take a beating and keep on ticking. They were a favorite of service men in Vietnam. When other rifles just wouldn't work the M14 just kept going and actually saved lives because it was often the only rifle still running in the squad but that's a story for another day.
Naturally a clean rifle is a happy rifle. Everyone that will ever come in contact with this article will already know that. So I won't go on about that. One thing I to want to discuss is lube. From the days of the M1 Garand these rifles were designed to run with grease. The biggest place for this is the Operation Rod Spring. The easiest way to apply it is to put a liberal glob on the op rod where the spring enters it. Then slowly spin the spring through the grease until it is fully seated. Clear the excess away and use it elsewhere.
These rifles are built so well there is little that goes wrong with them. It would be a good idea to keep a couple Op Rod Springs on hand. This will be the first thing to wear out and when it does it caused problems throughout the action. You see it is this spring that closes the action after it's been fired or upon loading. If this spring doesn't have enough strength the action wont close all the way, the action is disconnected, and will not fire. That spring is everything. One other to keep things flowing nicely is the extractor spring. They rarely wear out but cause problems when they do. A replacement is a good idea.
Keep it clean, including the piston (no oil or grease on the piston ever). A bronze brush is the easiest way to keep the piston alive and well.
Ok, we're done here. You are now all but experts on the M1 down to the M1A. Hope you enjoyed the article and found it informative.