I was curious and checked the list of gunss used by germany uk usa etc and they all used massive cartridges compared to todays standards even though protection nowadays is way ahead of what was available back then.
Most of the guns that use(d) big cartridges are bolt action rifles or semi automatics but a lot of the german machine guns (like the MG42) used the same ammunition and had massive firepower.
I understand that is simple to use the same type of ammunition for a variety of guns but the cartridges got smaller over time until we got to the point of the 5.56NATO ammunition.
I also understand that recoil is reduced so gun control is better, however, the level of protection (bulletproof vests etc) went up, which seems like counterproductive.
I also have some ideas in mind why it could be like this:
The trade-off is simply worth it. Protection is good but 5.56NATO is enough to deal lot of damage to a target.
Globalization led to newer laws which (at least tried) to get implemented and since targets nowadays (in a war zone) should not get killed but incapacitated we now have guns that don't aim for high damage but for accuracy and "getting the job done"
I hope I am in the correct subreddit but, since I am interested in the history of guns, I think it should fit here.
(Disclaimer - I'm sourcing a lot of this without materials to hand, finding references online, but this is well discussed and should be uncontroversial)
I think you're missing some of the point of why we use the smaller bullets - they're not less effective. In this post you're suggesting effectiveness is the same as firepower, which is not the case. A .50 to the face or a .32 to the face will almost always achieve the same result - death. Neither is more effective than the other until you add something to the equation.
Additionally, more bullet does not always mean more wounding potential - the 5.56mm round was in fact designed with a brief that specified equal wounding potential to the .30 round it replaced. (https://web.archive.org/web/20040209030852/http://www.thegunzone.com/556dw.html) - It achieved this by, as a lighter bullet of a certain shape, destabilising more dramatically upon entry, tumbling and causing a larger wound cavity than a larger bullet achieved by passing straight through a target. Hollowpoint pistol rounds work in much the same way - they split and expand upon entry to ensure a larger permanent cavity in the struck flesh than a solid projectile of the same size would achieve.
In terms of infantry however, effectiveness is determined by more than firepower. Firstly you have logistics. Smaller bullets can be made in greater number with the same amount of materials. They can also be carried in greater number and you can fit more of them into a weapon because they're lighter and smaller for the same number of shots.
That alone makes it preferable for militaries to use the smallest calibre bullets possible that are still potent enough to achieve a reliable kill from whatever distance you might be engaging at. This is why submachine guns use pistol calibers and sniper rifles use larger calibers - they aren't trading off kill potential per bullet at all ranges - only the ranges the weapon is not designed for. In return for giving up long range power, SMGs gain higher rates of fire and larger ammo capacity in close range engagements. An anti-material rifle makes the opposite trade, and an AR seeks to occupy a versatile middleground.
A good place to read more about why a larger round likd the 30.06 was not that middleground, would be the development of the M1 Garand, and it's closest competitor in military trials, the Pedersen T1.
Ultimately, the M1 Garand won those trials as a 30.06 caliber weapon because Douglas MacArthur spoke out strongly against a change in caliber to .276, as a result of there being extensive stocks in circulation already of the larger 30.06 cartridge. (Fitzsimons, Bernard, editor. The Illustrated Encyclopedia of Twentieth Century Weapons and Warfare. (London: Phoebus, 1978), Volume 10, p. 1088, "Garand".)
But originally, the .276 calibre was selected during trials as the best compromise between the factors listed above - size, weight, stopping power, range. The performance of the rifle in trials was equivalent to the 30.06 variant of the same weapon. (Walter, John (2006). Rifles of the World (3rd ed.). Iola, WI: Krause Publications. p. 143. ISBN 978-0-89689-241-5.)
The Pedersen on the other hand started and ended it's life as a .276 calibre weapon - Ian McCollum from forgotten weapons has many great historical videos on the Pedersen, and in most of them he explains that the gun, while good, has minor foibles the M1 does not, but that what killed it's chances in the trials was less those foibles, and moreso, the change in spec from .276 to .30 after MacArthur's speaking out. The Pedersen simply wasn't a design that scaled as easily as the Garand did, and so couldn't be reworked as quickly to fit the new brief.
That would remain the primary reason to stick with 30 caliber rifles all the way until 1968 with the M16, which was subsequently introduced with the substantially smaller 5.56mm bullet diameter we discussed above - which had equal wounding potential, but now came with the sizable logistics advantage of a smaller, lighter, more plentiful bullet, with the enormous post-war stocks of the 30.06 round having now been decreased and worked through to a point whereby replacing the standard infantry caliber could be done without obsoleting massive quantities of existing ammunition. (And of course, a new military pact helping the process, and ensuring that logistics were further improved by being able to share supply lines with allies, instead of having to deliver US-Specific ammo to combat areas)