Your right if your talking about going to a 7.62mm round but what if there's a 15% improved chance of stopping a target with a 6mm or 6.5mm round. Would the extra weight be worth it? To me that's the big question. How many lifes would be saved by that 15% improvement? How many less rounds could you carry if they were 6.5mm?

That is a more complicated equation, but it still runs into the fundamental point that, with current technology, we're just pushing around pluses and minuses.  I'd have to wonder that if every life saved by throwing a bigger bullet would not have a corresponding life lost because the shooter only had 25 or 26 rounds in the gun (or a smaller basic load carried overall), or was slightly slower transitioning to new targets due to recoil, and such.

 

 

I'm not saying you lose one for reason B for everyone you save for reason A, but just that "bigger/heavier bullet" does not carry zero liabilities along with the plus of more thump on the bad guys.

 

 

I think that the recommendations that we keep what we've got as long as we're shooting cased cartridges makes sense (and I say that as enough of a fan of 6.8mm Rem SPC that I own a 6.8mm AR).  If/when (and it looks more like a 'when' at this point) we see the technology jump from conventional cartridges to caseless or cased telescoping ammunition, I'd hope we take a hard look at formulating an ideal small arms round, the hits an optimal balance of bullet weight, caliber, recoil, muzzle energy and the like.  It may be that 5.56mm puts in a good showing (caseless or CTA lets might allow use of heavy 90 grain rounds which currently are tricky to get to feed through an AR magwell), or it may be that something else seems preferable.  I personally suspect that we won't see anything smaller/lighter than 62 grain 5.56mm selected, but it would be interesting to see what a blank slate, with no logistical tail or existing stocks of weapons and ammo to contend with, would result in.

Not new round need a new weapon.

 

You shoot at a guy four times and all you get is four rounds with a weapon that is capable of semi-auto fire.  The M4 has a tendancy to jam on semi-auto fire.

 

Even when you don't fire the thing get's dirty.  Being in the sandbox makes it that much worse.

 

We need to stop buying anymore of these crap guns.

That is a more complicated equation, but it still runs into the fundamental point that, with current technology, we're just pushing around pluses and minuses.  I'd have to wonder that if every life saved by throwing a bigger bullet would not have a corresponding life lost because the shooter only had 25 or 26 rounds in the gun (or a smaller basic load carried overall), or was slightly slower transitioning to new targets due to recoil, and such.

It all comes down to how much better the bigger round is. If you can carry a 1/3 less rounds but only need 1/2 as many then you come out ahead. But if the larger round is less likely to jam that's something to think about too.

Please explain how the size of the round determines whether the gun jams?

What Yimmy said, though a light construction, super high velocity round would have some merits inside, say, 100-150 meters or so (that is, essentially, what the FN 5.7mm round is, for instance).  You bleed off energy rapidly with a light bullet, though, so it would probably not work for a 0-300 or 0-500 meter sort of cartridge for a service rifle/carbine.

Why would you want the bullet to be light?

You want the bullet to be as heavy as possible for its given size, so that it retains its momentum and energy down range.