Lots of pistol suppressors released recently, it's a good time to be in the market(as long as you're patient as many are sold out). Make sure whatever you get you can get an adapter for your various thread's, SilencerCo's adapters are used by some and very abundant - newcomers(even some designs that have been out a while)... not so much. For your 300 you can either get a Fixed Barrel Spacer that goes in place of the piston spring to disable movement or you can get a fixed mount.
I went with a SiCo Octane .45 HD out of the choices a year or so ago, I am satisfied with the suppression level and ability to get whatever adapter I desire - their customer support is supposed to be awesome(apparently the cover 'stupid', once) but I've not needed to utilize it yet. One of the reasons I got it was that a 9mm cap was offered - however it turns out to be a PITA to change out and doesn't provide any distinguishable benefit with 9mm. I like it being user serviceable in case I shoot lead reloads thru it allows me to clean it out. I experience more backpressure that I would like, but not having any direct comparisons that may be normal.
These days I would look hard at Rugged Obsidian or Dead Air Armament Ghost-M due to their ability to be configured long or short. The Ghost has the ability to use an additional sacrificial material called a wipe to reduce sound more if desired. Truthfully I haven't said to myself 'I wish this was shorter and louder', but it's a nice feature to have.
Another one that has been getting good reviews is the Alpha Dog. While I think it's pointless to have a rail on a can, it apparently does a very good job of reducing heat buildup. They also seem to not have an issue with First Round Pop which can be an issue with monocore designs. I'm not a fan of eccentric cans either as they limit mounting options, but apparently it can keep the can from unscrewing if put in the 'down' position, so there's that...
Lots of data on SilencerShop.com and they will have by far the easiest way to purchase a suppressor once their kiosks to take fingerprints are installed at dealers. Some of SS's data is available on this spreadsheet:
https://docs.google.com/spreadsheets/d/1qBIkgmxQBVyP2ppC3-dWMjzneivmLkQ39VuZfW3gAjs/edit#gid=230029003A couple items when shopping:
-Be realistic about how the can will be used - there is no 1 can that does everything - there's always tradeoffs. Outline your priorities(weight, cost, ability to shoot rifle cals, mounting system, suppression) and let that lead you.
-Don't chase numbers. Without going into too much detail you won't notice the difference in 3db. Some say tone is more important, which is unfortunately impossible to determine without physically being there while a can is shot. Not to mention there's lots of environmental variables that come into play making it very difficult to get valid A-B comparisons.
-When looking thru YouTube reviews, take any tests/observations from a microphone with a grain of salt. They have a limited range and response that are not suited for gunfire. The only way to get valid data is with a very expensive Sound Meter.
-Get ready to wait. If your suppressor is out of state it can take 2 months for the ATF to approve shipping it between FFL's. If you started your transfer back in February you might be getting your stamp now(5 months later), but due to a recent law change there have been a record number of purchases - some are guessing that it may take a year to get a can that was purchased today.