"battle rifle" is common umbrela term for old ww2 rifles using the more powerfull cartridges
as the war doctrine of the time dictated the need of weps capable of 500+ meters lethality
after the war it was observed most gunfight were in the 100-300 meters range so the intermediate cartridges as 7.62x39 and 5.5 derivates were adopted alongside of the "Assault rifle " doctrine
so penetrating power of "battle rifles" and most medium machineguns is nearly identical becasue they use largley identical ammo , yet machinegun ammo thou similar in dimesions tend to have more powerfull propelant beacause they need extra kick to cycle the mecanism witch in most cases is either recoil or gas operated.So generaly speaking mg have more penetraring power.Heavy MG dat use 13mm and above cartidges are comparable in penetration and balistics to antimaterial rifles but due to their more sturdy construction longer barels and availabilty of stronger ammuntions MG tend to perform better than the rifles
M2 as a sniper rifle[edit]
The M2 machine gun has also been used as a long-range sniper rifle, when equipped with a telescopic sight. Soldiers during the Korean War used scoped M2s in the role of a sniper rifle, but the practice was most notably used by US Marine Corps sniper Carlos Hathcock during the Vietnam War. Using an Unertl telescopic sight and a mounting bracket of his own design, Hathcock could quickly convert the M2 into a sniper rifle, using the traversing-and-elevating (T&E) mechanism attached to the tripod. When firing semi-automatically, Hathcock hit man-size targets beyond 1,800 metres (2,000 yd)—twice the range of a standard-caliber sniper rifle of the time (a .30-06 Winchester Model 70). In fact, Hathcock set the record for the longest confirmed kill at 2,250 metres (2,460 yd), a record which stood until 2002, when it was broken in Afghanistan by Canadian Forces sniper Arron Perry.[52][53]
ps better internal dmg is best achieved by 5,5 caliber ammo variations dat have offbalanced bullet and lower powder charge , combination of these 2 things causes the bullet once entered the body to thumble and rickochet from denser surfaces such as bones causing way greater dmg than strait piercing more powerfull rounds , bad side of such ammo is low pentration , bad balistics , and its notorious unreability when used in battles involving dense vegetations because even pencil sized twigs tend to send the bullet offcourse