Really easy to get into if you already have a 5.56/.223 AR.
You can use the same lower, bolt carrier group, and charging handle. You can even use the same mags although I don’t recommend doing so.
All you need is a 300 blackout upper, which you can get for as little as $200.
The link below is to the upper I use.
https://palmettostatearmory.com/psa-...no-bcg-ch.html
Most common 5.56 rounds are between 55-77gr. 300BO range from 110-220gr subsonic rounds. The difference in energy delivered is pretty substantial.
Edit:
If your AR lower has a stock you’ll need to either swap it out for a brace, pay $200 for a tax stamp to SBR it, or take your chances, since the 300 upper is only 7 inches (making it legally a pistol), or you could just buy a 300 upper with a 16 inch barrel.