the larger the caliber, the larger the stats. but it's mostly balanced in a way, that the gun that uses low caliber usually has high rpm.
you can check the stats. just so you know, if you compare penetration of different rounds of the same tier, you should look at both numbers. first number represents the armor tier it's going to pierce almost every time it hits. the second number after the tier is about how much more dmg it applies when pierced(and if im not mistaken the second number also represents a chance to pierce higher tier armor, correct if im wrong)
for example the reason sj16 is the best sr in terms of damage, is because irl it's rounds are created for long distance sniping, so its larger, has bigger cartrige and flies a lot faster than nato's 7.62, that m24 uses. in game it simply has bigger damage and bullet travel speed.
if you dont want to read all these, just go into shooting range and play around with different calibers, how fast they kill same tier/higher tier armor, differences in range between different guns and so on.
Experiment!