I'd like an HK-91, just because I had a chance to shoot an HK-91 with a registered sear. Full-auto .308 battle rifle is pointless, but still a giggle. With the current cost of .308, a .308 rifle that mangles its brass the way an HK-91 does isn't terribly practical, though.
I've got an AR-10, M1A loaded, and a FAL. Out of those, I'd put the FAL last.
A lot of fan boys say the FAL is great because of the adjustable gas system. They claim that the adjustable gas system makes it better because you can adjust it. What they don't tell you is that if you adjust it wrong, you can turn your FAL into an awkward club. I know, because I've done it.
I'm the dolt who didn't follow the directions and adjusted it wrong. Without enough gas going to the piston, the bolt carrier will short cycle and the cartridge case won't be fully extracted. In my case, the cartridge case got jammed between the bolt carrier and the dust cover. It was jammed in hard enough that I couldn't cycle the charging handle. And without the bolt carrier able to go forward, I couldn't unlock the upper from the lower. And without being able to unlock the upper from the lower, I couldn't remove the dust cover.
If you adjust the gas system the other way -- put too much gas to the bolt carrier -- that can be just as bad. With too much gas pressure the gun will cycle too fast and call pull the head off the cartridge case, leaving the rest of the cartridge case in the chamber. If you don't have a cartridge case extractor tool, you're screwed.
Now, is adjusting the FAL gas system "hard"? No. Here it is:
Operation 1: Unscrew the regulator sleeve from the gas block until it is in the fully open position with “7” visible on top. After inserting an empty magazine into the rifle, single load a cartridge through the ejection port and then fire the rifle. This should result in a short recoil that does not allow the magazine to engage the hold-open device.
Operation 2: Screw the regulator sleeve forward click-by-click, firing one round after each change until the action is locked open by the empty magazine. At this point, you know enough gas is being allowed against the piston to cycle the action.
Operation 3: Fire several more rounds in this method to verify it will reliably cycle the action fully.
Operation 4: If any shot results in a short recoil failing to lock the action open, click the regulator forward one more setting and test again.
Operation 5: Repeat operations 3 and 4 as needed until the rifle cycles reliably.
Operation 6: The correct gas setting should now be determined. However, it is a good idea to click the regulator forward two more settings. For example, if you found that setting “4” cycled the rifle, click two more positions down. Counting the half-position setting between “4” and “3,” this would put you on the “3” setting.
On the other hand, here is the M1A's procedure for adjusting the gas system:
Yup, you don't have to adjust the M1A's gas system -- it just works. Sometimes simple is better than more complicated.
As for how the gun shoots, I find that the FAL trigger is pretty horrendous and the sights are primitive. The FAL receiver is quite long, putting my support hand way out there. It just isn't comfortable to shoot offhand.
In contrast, the M1A has a great trigger, fabulous sights, and balances nicely. It just feels right in my hand.
If you want to scope your .308, the AR-10 variants are better for that.
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All you need to do is pick the two of them up to appreciate the difference.
There is a reason that the FAL is called the right arm of the free world and has been adopted by almost 100 countries as their main battle rifle.
I own both an AR-10 and a FAL. If forced to choose between the two, I'd take the AR-10 every day and twice on Sunday.