There are many choices when it comes to scopes for a M1A rifle and the only homework you would need to do is to figure out what suits you best and what are your needs. When it comes to scopes, there are several things that you need to consider from its eye piece, to the eye bell, to the elevation adjustment to the objective lens. All these things, and many more need to be according to what you want and how you would like your scopes to be like.
Rifle scopes are important as they magnify an image and put your eye on the same optical filed as the image you are viewing. With scopes, and image is magnified through a series of lenses within the scope. Generally, lower powered scopes are typically shorter with smaller lenses than high powered scopes.
When choosing a M1A scope, consider these two items- the field of view (FOV) and the magnification of the M1A rifle scope. With the FOV, it is basically what you see through the scope when you look through it. The wider the FOV, the better you see.
When it comes to magnification, some have variable power while some have fixed power. If its fixed power, the label on the scope will read ‘4x’ meaning that the scopes magnifies an image by four times. On a variable scope, you would find ‘3.9x, 50mm’ which means the scope enlarges the image between 3 to 9 times more, with an objective lens of 50mm in diameter. For M1A scopes, having one that is variable is nice. It allows you to adjust the magnification of an image to the situation you are in- whether in the morning where you need less power of in the afternoon where you need more power.
The disadvantage of the M1A rifle scope that is variable is that they are generally more expensive than their fixed versions and fixed versions require more frequent sighting in. Anyways, if you can afford a variable M1A rifle scope, then get one.
Apart from the magnification and the FOV, you should also consider if the M1A rifle scope is sealed, water and fog proof. A good quality scope can withstand water and fog for a longer period. Lens coating also is a very important aspect of your scope. Make sure that the scope you buy has coated lens to protect them from scratching, reduce glare and improve resolution.