TTBB- while I love my FAL I think it is far from perfect. I think you are decovering some things that are not great about the rifle, again nothing is perfect.
A. There is non-recipracating bolt handle on a FAL, therefore no way to "forward assist" the bolt (Izzy excluded) That is why the bolt needs inertia to work correctly. It was desigined that way! By trying to achieve somthing the rifle was not desigined for you are changing the bolt speed, which will wear parts out faster thru exissive battery, and possibly be dangerous (slamfire).
B. The gas system is adjustable so you can give it more gas if it needs it, that means when it is new and rough, or old and worn out, or dirty, or bad ammo, ect. This can be VERY hard on brass, espically commerical brass. I have had many different rifles that reguire no adjustments, and little cleaning (M-1,M-1car,M-1a,AK,AR...ect)so I dont like the adjustable gas system, but that is what the FAL has.
C. You have allready experanced some of the problems mounting the rear sight on the lower reciever causes, expect accuracy to suffer also.
Everything has pluses and minuses, and you can midegate many of them, but if you get to gung-ho with a dremmil tool with out really understanding the entire system problems can result.
On top of all this it is a semi-obselete REMANUFACTURED Main Battle Rifle (DSA, abet one of the best ones) but not a FN, or even FN licenced, or assembled from all new hammer forged parts by FN licenced armorers.
Dont worry about reloading your brass, dont expect it to be a tack driver, dont think its going to run like a swiss watch. Expect it to run like a tractor.
So expect some problems with your new (old) rifle, have fun learning about fixing them, but most importantly get out and shoot it.