My program was to equip with an AR-15 lower with swappable uppers.
.223 barrel for out to 300 m
.308 barrel for up to 800 m
.338 Federal for 800+ m
Sniper kit only has to carry two extra receivers and another 100 to 200 rounds. BTW, most snipers I have spoken to about this arrangement say “pass ... too much weight”
I mention all of this because the “obvious” solution is often not acceptable. The reason .308 was chosen was be cause it had good kill vs range. I should point out that you can lengthen the .308 barrel and get .300 win mag performance out of a .308. This is how the M44 (7.62x57r) is able to achieve good performance. Though as a new system, normally only held 2 to 3 MOA. Might have to repackage into a bull pup to keep the length manageable though.
However, special situations require special solutions.
The same bottoms will work with both 223 and 30 cal tops?
Nice way to kill our troops. The reliability of the system is already questionable....using uppers not designed for those lowers will simply lower the reliability.
We're talking sniper rifles here, not battlefield weapons.
M24 in .300 Win is OK, but still insufficient for extra long-range. That is why the Brits use the .338 Lapua for sniping and we use the .50 BMG for sniping.
Won’t work in an AR-15. It might work if you used an AR-10.