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??