Post moved from Made in Singapore Equipment to this relevant thread.
A follow-up question.
I recently watched this video on the US trials for a 6.8mm rifle and round (and another on the trials for a .338 MG) from Task & Purpose.
If, in 10 years, the US moves to a brand new 6.8mm cartridge, would Singapore follow suit?
I'll leave this here, as it is related and pretty informative (aside from the menial meming here and there).
The US Army has stated previously it will only replace the current service rifle if technology has offered an improved enough product. The use of polymer/composite based ammunition is certainly a weight saver, though as stated Sig Sauer is betting on not upending the ammunition industry in the US - can't comment, might depend on how important the industry is to certain politicians.
At the end of the day though the initial purchase of the weapon is not a replacement, it only seeks an initial (albeit large batch) to insure the weapon meets requirements before committing. Until a supply chain can be set up for the new weapons and their ammunitions, the 5.56 will continue to be employed in large numbers by the US. To any US ally, it would be logical to continue employing 5.56 in order to maintain interoperability and to tap into that supply chain.
It depends how interoperable Singapore wants to remain with the US and how willing it is to invest in what is arguably a modest gain. As noted by others there are other factors. Barrel length is one, depending on circumstances though likely to be shorter for SAF, due to their emphasis on urban warfare and less on stand-off firefights. As also noted by sgtgunn, rounds within 100m become less of an issue.
I think it is interesting and worth considering down the track, but until a supply chain and suitably equipped force has been created it is unlikely. The US appears to be doing this with an initial order, though there is room to not commit.
5.56mm works for the job that needs done. It is lethal and comparatively light (putting aside polymers/composites), whilst at the same time being compatible with a wide array of weapon systems. I'd argue the weapon design, the training of the operator and enhanced tactics are more pertinent to the success of a battle.
On a side note, the situation may be different if we are going back to Afghanistan. Long range firefights and weight reduction in ammunition are more favourable there, evidenced by some Aus SOTG guys going out with AK and PKM systems when it mattered. Still most of the firefighting and the vast majority of missions occurred in urban environments.