I've heard conflicting reports about not being able to attach a bayonet to a 16" M4 barrel.
Whats the skinny on this?

Also, I've heard the mention of some sort of adapter/special bayonet, but I've yet to find either; do they really exist?  If so, where?

Finally, do bayonets only work with the A2 birdcage flash hiders?  Or will they also work with a Smith Ent Vortex flash hider?

Sorry for all the questions, but I'm trying to decide what to do with my postban 16" M4 profile plain barrel.

1) get postban barrel threaded for A2 / Vortex flash hider (no bayo lug)
2) buy new pre-ban M4 16" barrel from Bushmaster
3) buy new pre-ban M4 14.5" barrel w/ perm. attached Vortex
4) Any other suggestions?

I'd go with Option #3.

As for bayonets on a 16" barrel, there is a custom one made to fit since the standard ones will not.

CLICK HERE