RPK damage working as intended???

I noticed recently when using the RPK and confirmed it later in the firing range, that at 10m it only does 27 of its 33 base damage, and then at 15m it goes all the way down to 21, and anything past that 20. The M60 for instance with the same base damage and similar rate of fire does 33 damage at 10m and 25 damage 15m and beyond. 

All of the 25 base damage LMGs have a 4 shot kill at 10m and 5 shot kill 15m and beyond, I feel like that RPK shouldn't also be a 4 shot kill at 10m and 5 shot at range, but should follow a similar damage model to the M60. 

Anyone know if its working as intended or if its a bug?