Has anyone tried dpms bayonet adaptor that clamps on the barrel? Would this work on a 14.5" barrel? Could someone post a pic of one clamped to the barrel so we could see what it looks like?

A 14.5" barrel is made to take a bayonet. If you have a lug in the right place, under the FSB you're good to go. If you don't then adding the clamp on adaptor would shorten the distance between the FSB and the muzzle device and may make the bayonet unusable. (It may then be to long to hang on the FH) The adaptors were originally made for the 16" barrels. You'll just have to try it and see.