[OrdnanceGuy]

Does it damage the gun when it blows a primer?

It could easily damage the gun. Things like eroding the bolt face, blowing off the extractor, firing pin, etc. :scared:
It could also damage your body, eyes and such. :scared:

Interesting. I read recently that crimped primers were required to keep blown primers from causing FA fire malfunctions, esp. with belt feds.

The crimp keeps the primer from falling out of the cartridge case and into the internal parts of the gun, leading to a stoppage. A crimp would not stop a primer from being pierced, however. A pierced primer might allow the gases into the breech area, just like a (completely) blown primer might. :hatprop: