Wow ah! Somebody call the Marine Corp! This thread proves light rifles are just as accurate as heavy ones!
C'mon. YMMV, but IIRC, a heavy 12-15lb rig in my hands shoots much better prone, from an improvised rest or even standing... The weight dampens vibrations, heartbeats and instabilities. In general, all accuracy sports have a max weight rule because weight IS such a huge advantage.
Wait...don't they prove this at Camp Perry annually??
When you are in a target shooting situation, or military sniper taking 1,000 yard shots the difference between a .2 MOA 15 lb rifle, and a .3 MOA 6 lb rifle makes a difference. For a deer hunter @ under 500 yards the extra .1 MOA is not worth the weight. In fact from typical hunting shooting positions you can't really take advantage of anything much less than 1 MOA.