Make bullets do a lot of damage fast
Make people have lives and have to wait for rounds to reset
Present maps and weapons in a way that it rewards players for keeping other players suppressed by fire
if you dont want people to jump crouch and arena-fps around out of cover just remove jumping
Focus less on making 'bullets scary' and more on making mechanical design revolve around making the bullets indirectly scary by heavy and obvious consequences that punish the player when they do not use strategy and play intelligently around the meta of your gamemode
If you want realism go play Squad or some stuff.
unfortunately this post is not helpful or meaningful to anyone