I took her out today. Indoor range. Had three fellow shooters three lanes over. They all felt the concussion from the 7.5" FSC556. They were shooting 30-30, .308, & 45-70. I was using Fed .223 and had a little back blast. Not too bad.
I switched to Fed XM193, and there is without a doubt a fireball out the front of that FSC556. Back blast more noticeable as with the heat. Still pretty fun, I'll have to take her outdoors to get the full effect.
A Noveske KX3 will be added later.