We see how well it fares against that in FO2, with the Gauss rifle doing basically the damage an ingame .50 should do (corroborated with NV having .50 and gauss doing similar damage).So..mid caliber rifle rounds. Something normal body armor can stop.
It is impressive but unless we see how it deals with 50 caliber munitions or 50 caliber SLAP rounds or stronger
The answer? Not well at all, goes through it like butter.