I enjoy shooting subsonic cartridges. I have the 300 whisper, 338W, 510W and the 458 socom, as well as suppressors for all of them. The 300W and 458socom are loudest because they are on the ar15, which has lots of action noise. The 338 whisper is the best, followed by the 510 W. The 50 cal can is 2x18" though, rather big. The comparitive noise levels are all subjective by me ear, I do not have a good noise meter. I was also able to fit the 50 cal can to an enfield converted to 45 acp. 14" of the barrel is enclosed in the can, which ports into the barrel the last 6".
I am considering making a can for the my M1A, but it will have to wait until I finish one for my heavy barrel savage 308win. Large powder charges and action noise add up to noise levels that are not ear safe in the long run. The sonic boom does not seem to be much at all, just noticable, but then most of my hearing loss is in the higher frequencies, but I can hear between 0-15 decibels across the tested range even after 20 years in the Navy. Even if shooting does not hurt, it can still cause hearing loss.
Ranb