Penetration is a big part of ammunition's performance, it would be sad if this aspect of the game stays badly simulated.
The lowest mass military grade 5.56mm is the 4g (62 grain) SS109 FMJBT with muzzle velocity of 940 m/s. Here is a video showing lower mass 55 grain 5.56mm FMJ bullets penetrating 1/4 inch (0.635 cm) of steel into ballistic gel from 200 yards (183 m):
https://www.youtube.com/watch?v=50_3Yyo0Nt0#t=190
Considering this and the fact metal panels used in the shack are no more than 0.05 inch (0.127 cm) thin, the penetration capability of the 5.56mm (and probably other cartridges aswel) should be way higher in Arma 3 than it is now.
Edit: The muzzle velocity info in the pic is false, should be 75-100% for the red bullet path, not 50-75%.