This is from memory, so please forgive any errors...
The M1a, standard, 20" rack-grade rifle weighs in at about 8-3/4 pounds. I assume that the shorter-barreled versions, the M1 SOCOM and such, would be lighter.
The Armalite AR10, again with a standard 20" barrel, runs a bit over 9 pounds. If you build an AR10 with lightweight components, you should be able to get the overall weight down to around 8 or 8-1/2, maybe less.
FALs and HK91s in standard configuration both tip the scales at around 10 pounds. Lightweight versions do exist, such as the old DSA SA-58 Lightweight Carbine, which was supposed to weigh under 8 pounds. Impressive...
Pay your money, take your chances.
- Chris