[HorseSoldier]

A .30 caliber rifle with iron sights is not much of an advantage over a 5.56mm rifle or one of the Soviet x39s -- you'll almost never be able to acquire and positively ID a target for the added range to matter, and then no one, even with lots of training, manages to make those longer range shots with iron sights with anything more than statistical static on two way ranges.

There is, ultimately, a reason why everyone on the planet quit using 30-06/308/8mm/etc full power rifles in favor of assault rifles. Assault rifles just work better for real combat. At the ranges where you can actually pick out a target who is not being really cooperative in assisting you in killing him (i.e. walking towards you in open order, WW1 1914 style) the assault rifle/intermediate round combo has all the range and hitting power you need.

I've read stories over the years of the Soviets being at such a disadvantage versus Afghans using Lee Enfields in the 80's.

Mostly just mythology. The Afghan Muj took to the AK like junkies to a free supply of heroin, once we started getting serious about supporting them and shipping them real weapons. When they were armed with Lee Enfields (which they had and which we gave them before we were serious about screwing the Soviets) the Soviets mostly mopped the floor with them anywhere they raised their heads.

With rare exception, I would think fire discipline would be a way of life except in dire emergencies in 2000 AD for infantrymen.

They also do a lot more walking than real life infantrymen, and being able to carry twice the basic load of ammo for the same weight means a whole lot.

M14's would be nicer (more due to magazine capacity, ease of scope fitment, and the whole Garand *PING* ejection than any full auto capability), but may not be as available at times, depending on the area.

Without the Cold War ending, the US government would have still had most of the million-odd M14s it bought in storage instead of blow torched and/or given away for free to new NATO members in the Baltic. I doubt they got recycled into DMRs in the Twilight War timeline a la real life, but would guess they might have gotten handed out extensively to local law enforcement, militia/state defense force units, and such (i.e. the guys the Small Arms Guide say got M16EZ kits). Maybe some on the late war USAR divisions as well, and some could have found their way to other units along the way, especially as the war gets hinkier and more disorganized.

Garands would be more problematic -- lots out there through CMP, but on the .gov side, not so much, and 30-06 was not a particularly supported caliber any more by the 1990s, militarily speaking. 30-06 ammo is real common on the civilian side, but loads that don't replicate the USGI load can bend the op rod on a Garand and deadline it completely, so it's not a weapon where you can shoot anything you can scrounge without aftermarket alterations.

Any thoughts?

Optics make a long range gun more than caliber. TA01NSN ACOGs were in service IRL before '96 in the SOPMOD kit and elsewhere, they could have been adopted more broadly in a Twilight era timeline where the Advanced Combat Rifle program fizzled but there was still Cold War style money floating around to try and improve service rifle lethality.

Basis of issue could have been greatly expanded on those, and the earlier Vietnam era Colt x4 power scopes might have been (re) adopted as well.