Since it's your first can I wouldn't go with the .45 cal. Thats probably one of the loudest, least suppressed calibers you can get. Although there are finally some hearing safe cans for .45, I think two models, it will make you not want to get another silencer. If just doing it to get suppression start with a .22, or 9mm so you won't be disappointed with the silence and you will want to order more cans. Beware though suppressors are an addiction as I have made 5 NFA purchases already this year.
9mm Para 163db(a)
.45 ACP 157db(a)
Isn't most .45acp ammo subsonic? I thought .45 acp was a great choice for suppressed fire specifically for this reason?
Also, isn't .45acp actually quieter than 9mm (I found this on the net)?
Or is that crack instead of boom?