People talking lot about caliber change is not that easy...simply it's PIA(Pain In Ass).
Reason if you want to change one caliber to another you need these things
1)Better guns and ammo
2)Infrastructure for making huge amount of ammo,because soldiers need alot of time and training for caliber change
3)And war wastage reserves.
Without getting into arguements and taking sides...
- Caliber Change for standard issue rifle for a country is indeed very expensive but countries need to do that to adapt to changing battle scenarios and to maintain OVERMATCH capability. NATO has changed from 7.62x51mm to 5.56mm as standard issue in past and is talking of going to 7.62x51
- When they talk about adding a new intermediate caliber like 6.8 SPC or 6.5 Creedmore, it's to replace existing calibers and not just add to them. For example 6.8 SPC can totally replace 5.56 x45mm as general issue, along with 7.62x39mm for counter insurgency...It's very lethal even from 8 inch barrels and it's replacing 9mm MP5s in many places for very very close CQC and for Personal Security Details(like SPG)......(Many US agencies have adapted it and even Jordan )...That's three calibers !!!
- So ideally, an army should be left with two standard issue rounds, 6.8 SPC as an intermediate and 7.62x51mm as a DMR / Sniper (there would be small requirements for exotic rounds like .338 Lapua and .50 BMG)...
- This should greatly simplify the Logistics, Inventory management and even manufacturing, as once the existing plants are retooled, the investment will pay for itself in double time.....
These are just my thoughts as a Technocrat with some practical expereince in the biggest gun market in world
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of course there are much more knowledgeable and experienced folks to comment on this...