I'm happy to help you on here but it might be better if we had a phone call.
When looking at silencers there is always a trade off. So using a 30 caliber silencer for your 300 Blackout will be louder, longer and heavier than dedicated 22 silencer. So for best performance you are looking at 2 silencers. One for the blackout and one for the 22. Not to say that you can't use the 30 caliber silencer on a rimfire but it will not be as effective or efficient. Also most 30 caliber silencers don't come apart for cleaning where 22 silencers do. And they need to come apart because 22 silencers accumulate a lot of lead build up.
Now as far as the process of buying one we handle everything for you and make it simple. The easiest was is to buy the silencer, tax stamp and trust. You will get a series of emails that you just follow the links and complete in order. Then you will visit a kiosk or get your fingerprints taken locally and mailed to us. We have an app that you can download and upload your photo. For a detailed list of instructions look here:
https://www.silencershop.com/how-to-buy-a-silencer