I’ve bought a new AR-15 pistol chambered in .300 Blackout. I was wondering what would be the better brands both subsonic and super sonic.
Looks great! 
I don’t know anything about .300 blackout ammo, but will offer this link as a start: https://www.pewpewtactical.com/best-300-blackout-ammo/
What are you planning on doing with it and how are you going to shoot it? I shoot my blackout suppressed and handload for it. I can suggest some bullets and powders I have had good luck with, but wont give specific loads. It has been my experience listening to friend’s blackouts who shoot factory, the factory ammo, even subs, are louder than handloads. Probably has to do with powder choice.
Well, I plan to do both but it takes a while to get the tax stamps for a suppressor. Will shoot supersonic rounds til I get the suppressor tax stamps.
You can shoot subsonics without a suppressor. I built my blackout and the time I was waiting on the paperwork to clear, I did my load development. Count on waiting a year. If I look at all mine, the average was 10 1/2 months from the time the ATF cashes the check, which is about a month after you submit your paperwork.
What suppressor are you getting?
You can shoot subsonics without a suppressor. The recoil is a lot softer and the noise is… “less” than supersonic rounds even without a suppressor.
Fortunately(?), there isnt the same HUGE variety of ammo that 556 enjoys. Advice as always is try a few and see what your rifle likes. I haven’t shopped much post-COVID so any prices below are pre-COVID
For Supersonic plinking/range ammo there are several good choices in the 110-120ish grains from Magtech, Sellier & Bellot, Remington. Anecdotally the mid-weight (around 150gr) don’t really do anything well. So either stay light or go heavy. The Magtechs (115gr OTM/123gr FMJ) have been good to me and are reasonably priced around $0.50/rnd
For Subsonic plinking/range ammo, I don’t have a lot of usage, mainly just trying it out. I’ve had good luck with Remington 200gr, Fiocchi 220gr, & Magtech 200gr all cycling well and being as accurate as anything else. The Remington is an internet fav for being accurate.
Supersonic defensive ammo…
- Barnes TAX-TX 110gr (not the 120gr), super accurate, expanding all-copper, lots of penetration (for HD maybe not wanted, great for hunting). IIRC, this is one of the few bullets designed specifically for 300BO. Pricey at $1.50/rnd if you can find it in stock
- Hornady 110gr V-MAX. Very accurate, fragmenting round. IIRC, the bullet is actually a varmint .308 bullet but at slower 300BO speeds works amazingly well. Commonly priced ~$1/rnd and (pre-COVID) Hornady sometimes sold these ammo boxes with 200 loose rnds for ~$105 so a little over $0.50/rnd which is practically range/plinking prices. Even at $1/rnd is a very good value.
- Fiocchi SST 125gr. Not a ton of info out there but looks promising. Was super accurate for me. Can be found for < $1/rnd even today. I would have picked this for HD but there weren’t enough reviews out yet compared to the others
The criticism against subsonic defensive ammo is that a 200+gr projectile at subsonic speeds sounds just like a .45ACP. No doubt, to get the “most” out of the cartridge for defensive purposes supersonic is best. But you can make an easy case (IMO) for saving your hearing and these subsonics will still defeat IIIA armor. Some folks will put a subsonic in the top 1, 2, or 3 rounds and then supersonics in the remainder if that doesn’t solve the problem. I’ve had some cycling issues with mixing subs/supers in the same mag, so if you go that route make sure to test thoroughly.
Subsonic defensive ammo… (I have not tried either of these, personally)
- Lehigh 194gr (supposedly the “best”)
- Hornady SubX 190gr (supposedly accurate, but questionable terminally)
@Harvey and others. This is primarily going to be my “the fecal matter really hit the impellor blade at speed”, car gun. So let’s call it a “get home gun”. So in emergency I’m going to carry a mix of magazines. So that I won’t just be counting on a Glock 30 and 3 mags.
I haven’t started looking at suppressors yet but that’s mainly due to not knowing whether I would be able to get the Daniel Defense or the Sig Sauer version.
I’d say then, even though pricey, I would load those mags with the Barnes 110gr TAC-TX round. Barrier-blind-ish (car doors, windows, etc), all copper projectile. I wouldn’t bother with subsonic rounds without a suppressor. But if you do get a suppressor, I’d suggest the Lehigh’s in at least one of those mags. That’s a lot of coin wrapped up in a car gun though so make sure it’s locked up tight.
For training, grab any of the range ammo I mentioned above that is near 110gr. I like the Magtech 115gr here