Not particularly concerned about shooting heavy OTMs through a short barrel. I've done enough of it.

It may not be on the approved list, but it wasn't designed for combat use and the fact that it was eventually approved for anything is a tribute to a few people that shepherded it through the system.

See Ken's post for a coherent discussion of pressures.

And for M855, you can't shoot it through an M16 or M16A1 because the 1:12 twist barrel wont stabilize the longer bullet.

M4s and recent M16s have a 1:7 barrel, although 1:9 will stabilize M855 just fine.