Times seem to be coming down, I'm betting 9 months for my F4 from Dec '18, and 7 for my F4 from May '19. Up until now I haven't waited over 7 months, and my last one came in in Jan '18 after exactly 5 months in jail.
The suppressed .300 BLK I've heard was at the range, so I had muffs on. Quiet but hard to give a comparison. Action noise from something like an AR will add a lot of sound at the ear over a bolt gun.
I can say that my .22 bolt gun with gemtec subs and a SiCo Sparrow on the front sounds like you dry fired it. Much quieter than my .22 Benjamin air rifle. .22 cans are a good starting point because the suppression per dollar ratio is very high, and everyone loves to shoot shoot them. .22's with subs and a can are the only firearms I shoot without single or double ear pro on.
I personally love shooting my tuned .223 AR through my .30 can. It's very pleasant with just plugs in, spits very little gas, and has the ballistics to reach out to fun ranges.