Look again. You were right the first time. The actual ratio is approx 200 5.56 / 150 6.8 / 100 7.62
It appears you transposed your 7.62 numbers. Weight of 7.62 M80 is approx 23 grams, not 32.
You are correct. I transposed the wrong cell in Excel. It is 24.96 grams which I rounded to 25.
The correct weight for 100 rounds of 7.62 is 5.58 pounds.
I'm still not sure how to quantify the difference in capability between 5.56 and 6.8 in order to show that the latter is enough better to justify a switch, though. I'm open to suggestions on that.
Combat has changed and the 5.56 round isn't cutting it anymore.
The enemy has changed by using body armor. Troops are coming up against barriers and windshields in urban combat.
The majority of combat in one arena is CQB so the military has adjusted by giving troops shorter rifles 14.5" barrels for regular troops and 7.5" to 10" barrels for SOF. So now you have a rifle that is great to maneuver around but has lost effective due to the loss of muzzle velocity.
Combat in our other arena is long distance where you need a round that will allow you to reach out an touch. I am sorry but shooting at paper targets from the 500 yard line isn't the same as hitting and killing a human target in cold weather type clothing at the same distance.
You now have suicide bombers hopped up on drugs that need to be stopped with one shot. A round is needed that will have stopping power and good fragmentation out of SBR in CQB, allow a shooter to kill at a distance, and penetrate body armor/barriers/windshields. Does this sound like 5.56 to anyone?
Once the switch to 6.8 SOF and infantry are issued one lower with two different upper receivers, one SBR and one carbine or rifle length so that it can be more tailored to the mission.
With the majority of other things changing in reflection of the current state of combat doesn't it makes sense to update to a round that will get the job done too?