I believe they used the Springfield as a sniper rifle in the Korean War and Viet Nam, before it was replaced by a specially modified bolt action type rifle.
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Carlos Hathcock
I have wondered for a long time how well an M-16 with a 24 inch barrel would do. You could leave off the flash hider and the overall length would not be that much more.
Adding a lot of velocity to those heavy .223 bullets would make them effective at long range. I know they penetrate well with just the standard M-16 barrels.
One could compromise and make it 22 inches with no flash hider and it would be about the same oal.