Kimio I'm asking is because I'm debating on building a 16" FAL PARA, the rifle probably will not be shot out any farther than 300yd 400yd
A 16" barreled FAL should serve you well. I have an M14 with a 4 groove 16.25" barrel with a 1:10 ROT. It's set up for a sound suppressor and is more accurate than I am. When compared to a 22" M14 barrel the reduction in MV from the 16.25" is nominal and will probably come into play only if I tried to shoot tight groups beyond 600 or so yards. I'm not trying to shoot tight groups with this rifle so it's of no real concern to me.