When I was collecting data for Inf-info.xls, I got a good picture on how the bulk values are set in Inf versus RL. To sum it up: most equipment have a correct bulk value if 1 bulk unit (BU) = 1/5th kg. Sometimes when a weapon is very weak, it's made lighter to encourage ppl to still use it. Stuff that the creators felt would make people annoying are heavier. Like ACOG and Claymore.
And staff that are very heavy are made lighter. An empty M82 weighs 12.9 kg, so it should have a bulk of 12.9x5 = 65 instead of 39. This way it would be so heavy that with the smallest amount of ammo and other equipment it would cause hopelessly heavy loadouts, or -as you want it now- they should have make bulk to affect speed less, so a total bulk of 100 would still be reasonably fast. Here, there would be two possibilities. A: no one would use the M82 because of the low speed it causes with a proper loadout. This is what happened with the M136, which is as bulky as it should be, but is marginally more useful than a single 40 mm round. B: they would have flattened out the speed dropping curve, so 100 bulk would have been still acceptably fast. But in this case everyone would have taken 20 or 30 mags for an assault rifle, because 70 total bulk would have been as fast as 50 is now. So: they lightened the heavy pieces. These are the Minimi, the RC50, the M82, the M60, and to some extent the M14 and the PSG1.
I hope I could help you.
And staff that are very heavy are made lighter. An empty M82 weighs 12.9 kg, so it should have a bulk of 12.9x5 = 65 instead of 39. This way it would be so heavy that with the smallest amount of ammo and other equipment it would cause hopelessly heavy loadouts, or -as you want it now- they should have make bulk to affect speed less, so a total bulk of 100 would still be reasonably fast. Here, there would be two possibilities. A: no one would use the M82 because of the low speed it causes with a proper loadout. This is what happened with the M136, which is as bulky as it should be, but is marginally more useful than a single 40 mm round. B: they would have flattened out the speed dropping curve, so 100 bulk would have been still acceptably fast. But in this case everyone would have taken 20 or 30 mags for an assault rifle, because 70 total bulk would have been as fast as 50 is now. So: they lightened the heavy pieces. These are the Minimi, the RC50, the M82, the M60, and to some extent the M14 and the PSG1.
I hope I could help you.
30 rounds would add ~0.35KG, but then the result is a mag that weights just as much as a loaded 5.56 mag which doesn't make a whole lot of sense but is not impossible either (I never used 9mm for anything).
