To maintain full accuracy and minimal spread with the Rokstedi, you have to wait about a second between shots. You'll find that if you don't go spammity-spamming, your shots will be true to their mark, and you can put people down in a few shots. I personally don't bother with the Muzzle Brake, since the gun's recoil already settles faster than its spread, and I use the standard mag to maintain full accuracy. Throw on a COGA/Greeneye, and it pretty much bridges the gap between ARs and LRs.
FRKN is just a terrible gun, and out-classed by the Gerund which can fire 3-shot bursts with the same if not better accuracy, and with a smaller pause between them.
I have no tips for the three-burst rifle but the Rockstedi is an extremely powerful weapon when you attach rapid fire, I would also suggest using the default iron sights and adding a muzzle break. If the FRN3K had a rapid fire option as well Im sure it would be tons more usefull.
From what I can tell a rapid fire Rockstedi is the perfect weapon for high accuracy gamers, Its always my secondary on Heavy builds.
Rapid fire?? As it stands the gun already has so much spread, that the recoil settles before the spread has time to. In that case, making it fire even quicker... seems pretty pointless to me. Unless you were going to use it for hip-fire... but even then, it grows to shotgun-sized after a few shots.