"...improved by free floating..." Floating a barrel on a modern hunting rifle guarantees absolutely nothing. Wouldn't on a BP rifle either.
The accuracy of a BP rifle would have been improved by using better bullets than a round ball of soft lead. Same as it did when rifled muskets were used. The Minié ball expended and sealed the bore better.
Military BP rifles had full length stocks to protect the thing when bayonet fighting. Same as any military bolt action used later. Mind you, a lot of it had to do with "That's how we've always done it."
An M3 complete with battery and power supply weighs 21.3 pounds with an effective range of 100 to 125 yards. A BAR LMG weighs 21 pounds.