I've been a FAL fan for many, many years - ever since owning a commercial G series FN FAL imported by Browning before 1968. I've sold them all now except for two: a DSA Congo Para and a DSA stainless SA 58 that has been a project gun for many years (shown below).
The full sized gun started life as a gun built by DSA with Israeli furniture and an Argentine barrel. The gun was marginally accurate, routinely shooting 4MOA+ groups with ball ammo. I decided to do whatever I could to shrink these groups to at least half that.
I started by having DSA mount a standard weight 21" "match" barrel and DSA's version of a Belgian Combo device. To my surprise, this was no improvement at all. No worse but certainly no better. As with many other FALs in my experience, unexplained vertical stringing was the main issue. I addressed every aspect of the gun I could to include a close fitting front hinge pin and a tight lockup. Since the upper and lower receivers were a matched stainless set, I had no worries in that department.
Over time I also upgraded the buttstock and forearm, as well as the rear sight. Finally, and after watching a bunch of high speed videos of FALs firing, I determined that a heavier profile barrel would stiffen up the entire platform, allowing the gun to shoot concentric groups without vertical stringing.
That led me to have DSA install one of their medium weight "match" barrels.
I received the gun today and after a thorough cleaning and a few pictures I took it to the range. The target on the left is at 100 yards using Portuguese ball and the picture on the right is using Serbian M118 which is an inexpensive version of Lake City Match using a 168 grain match bullet. It has proven marginally accurate in a variety of other gun but I tried it just to see how it would work. I worked just fine I think.
The Port ball shot about 3" but printed a nice concentric group without fliers.
DAG shot a little over 2" (the lines on the target are 2" apart) and the group was nice and concentric.
The Serbian M118 put 11 out of 12 shots into less than 2". The high shot was called out of group just after I shot it. The three on the left are the original sight in group before moving the group over to center it up.
Last, the slightly heavier barrel brings the guns weight up about a bit to 9 lbs. 14 oz. but the balance is much improved.