I know it is an old thread but thought this worth mentioning:
The FN-FAL is not a .308 Winchester. Although DSA does make them in .308, the actual military chamber is for 7.62 x 51 NATO
Which is a larger chamber and in military automatic weapons, usually cut even more generously to allow for dirt.
That means you can fire .308 ammunition in an FAL, but it will be a loose fit in the chamber, making it less accurate. From the numbers below you can see that a NATO cartridge can be almost 5 mils longer than a 308, and the minimum length fo a NATO cartridge is 1/2 mil longer than the MAXIMUM for a .308. This means that if you have set up an FAL for zero headspace (for accuracy) with a 308 chamber or 308 cart in mind...you may have a slamfire as soon as the bolt closes on the longer NATO round! Way to ruin your day. (And if you are not headspacing your rifle, you're not even trying to get the best accuracy from it.)
Cartridge- MIN head-to-shoulder MAX
.308W------1.624--------1.634
7.62NATO---1.6345-------1.6395
7.62NM-----1.630--------1.6315
The NATO round is spec'd at 54,000CUP pressure, also 5% higher than a 308W which is spec'd at 52,000CUP. Which means the NATO rounds are also almost intermediate between a 308 and a 30-06, especially if you are hand loading and you load them a bit hot.
These things very much affect accuracy. I can tell you that an FAL, or even a well-made AK47, can fire 2 moa right out of the box. But if you take a NECO firelapping kit and polish in the barrel of a new FAL (or any rifle) just military grade, not a DSA custom job, the stock FAL can shoot sub-1 moa all day long if you can. And having the adjustable gas knob, so you can match up to your ammunition, also is part of that.
Is an FAL a good deer rifle? Well, there are lighter guns. And more accurate guns. And if you are handloading, and have the gas mechanism turned off, the FAL is pretty much a bolt action rifle, no longer semiautomatic. The game warden is going to give you a nasty look for having it at all...but if you understand the rifle and how to optimize it, the odds are it can shoot better than the fellow using it.