I believe they did use silencers.
Of course they did. Only the Mauser from the TSBD was allowed to make noise (except for simultaneous shots at the Turkey Shoot Point, which sounded like a single shot). And only 3 noisy shots, otherwise, it wouldn't match the 3 hulls that Fritz staged in the SN. I'm still not sure how Oswald didn't get a single print on the MC's stalk, barrel, scope, mag, ammo and strap when he disassembled/reassembled it in the TSBD. And why would you keep a useless scope on the rifle especially if you were trying to make it fit into a paper bag and you knew you wouldn't be using it anyway?
No, the MC never took a shot because it was already planted in the TSBD by then. They shot some rounds into a swimming pool so they could plant an intact magic bullet and 3 hulls, which could be linked to the MC rifle. Otherwise, the Bug was right that the conspirators would never rely on Oswald with the MC alone to do the job. He was the designated patsy. Every good coup needs one.