Im more or less new here, so if this has been brought down before and killed please forgive me.
http://www.bvpservice.com:8101/14,5mm-12,7mm%20cartridges.html Here it mentions that there are 12.7mm AP rounds capable of piercing 20mm of armor at 750 meters range, and 14.5mm ones capable of reaching 20mm penetration at 200 metes range.
In game however, HMGs have penetrations of 0 or occasionally one, and lack AP rounds. A penetration of 2 would make them much more lethal, especially towards various light APCs vulnerable to them IRL. Naturally more modern APCs would remain almost fully immune, but it would still IMO make gameplay more interesting and realistic. Just a suggestion for further development.