So, Techguns seems to impropely apply damage to players. Because of this, next issues appears:

• Bullets ignore Draconic's Evolution armour's shield
• Bullets are unaffected by Projectile Protection enchantment
• Last Stand from OpenBlocks doesn't prevent player death if he takes damage from a gun
  and some other issues which i can't remember...

The last stand enchantment should be fixed by calling the appropriate event in the techguns damage system. The event was added to forge after the code was written.