One will be a typical AR-15 5.56/.223. The other I want to make .300 Blackout. I shoot 100 yards max and like to plink and shoot targets. I like soft shooters. I've got one lower nearly complete and I like 16" barrels. I understand there are some complications with the gas systems, springs and buffers to make a .300 Blackout run right. (I intend to reload for it, so I have some flexibility) Can ya'll give me some pointers as how to accomplish this?

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"He was kinda funny lookin'"

Last year I built a .300BLK pistol from a PSA 'kit'... I just used all the parts that came out of the box. Haven't had any function issues to this point, but don't have a lot of rounds downrange with it, and everything I've shot to this point has been subsonic because I built it to be a suppressor host.

What will make a reliable .300BLK will vary with how you want to shoot it because of the wide range of possible bullet weights and velocities. There is an entire forum dedicated to the cartridge, and I've found a few threads that have good info when I've been searching on specific topics.

I can say that .300BLK subsonic/suppressed is a LOT of fun to shoot, and very quiet, but it's basically a pointy .45ACP. My bolt action .300BLK is incredibly quiet suppressed.

I didn't have any problems just putting a 300 Black Out upper on a 556 lower. It has worked flawlessly. The gas system is on the upper and uses the same buffer, spring, BCG, and magazine. I only shoot supersonic, so can't speak to any changes you need to make to shoot subs.

What's the point of .300? It is because it's quiet with a suppressor?

At 100 yards with 16" barrel , your good with the standard carbine gas that is common in standard ar rifles.
The sub sonic loads of 200-220 grains at about 1050fps are really fun and accurate at that distance.
The only consideration you would have is to keep your barrel twist in line with bullet weight. In my case, all standard ar with carbine gas and a 1:8 twist makes it all happen with the 200+ grn bullets.

The fact that you load adds even more fun and bullet range. There are a range of powders to keep you interested.

The above experience is based on carbine as opposed to pistol and unsuppressed platform.

I don't know how you intend use it but my 300 Black Out on a 16" AR shoots well using the 125 gr Sierras at 2000fps loaded with AA1680 powder. I have killed 2 deer with this load and neither one went anywhere after being hit. Distance was close (40 yds) in the timber. I have had zero functioning problems and used just the regular lower parts. I bought the upper already built so do not know what parts it is built with.

With the blackout use the pistol length gas tube, not much gas with the blackout.

Most important thing in my opinion is to make certain you never load a 300 into a 5.56.

I use distinctly marked magazines for the 300, and check and recheck when I load those magazines.

I seem to recall that many of the available 300BO uppers have pistol length gas systems. Is that true or did I imagine it?

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Release the Kraken

I bought somebody's self assembled upper in 300 Blackout. On my AR's lower the factory ammo at 150 grain and supersonic works fine using 223 Buffer and buffer spring. But with factory Subsonic and my subsonic reloads, I change to a carbine buffer and trimmer a few coils off a standard buffer spring (one coil at a time until action worked reliable with factory subsonic ammo, then developed my reloads) I use Berry's 220 grain plated bullets and H 4227 powder in brass that I formed and trimmed from range pick up 223. (the exact powder charge is then dependent on your spring and velocity combination)

But if you don't use a suppressor, why bother? At that point you have a carbine with 45 ACP power, you may as well be quiet!

Ivan

I'm sure I'll dabble in subsonic, I probably won't use a suppressor (Expense I can't handle) but I'll probably keep the loads in the 2000 ft/sec range for most shooting. I shoot an SKS about those velocities and it's not objectionable.

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"He was kinda funny lookin'"

A 30 round 45 acp with shoulder stability, red dot, low recoil, and low muzzle blast makes a pretty good home defense tool. Especially for my wife... And unlike my SBR 5.56, it won't damage hearing with a single shot, even unsuppressed.

That said, suppressed, .300BLK is even more fun. The other day, I was shooting .300 subs out of my suppressed bolt gun at steel. With a little wind that day, guys 50ft behind the line told me they couldn't even hear the report, only the ringing of the steel.

I like the cartridge for its flexibility, though it obviously isn't really excellent at anything. I don't hunt, so it's mostly just for fun, for me.

With bullets on the lighter side the 300 is not far behind a 30-30 Or 7.62x39, and with subsonic rounds and a suppressor very quite. Not sure I would own one if it I didn't have a Can for it.

Easy to reload for. I bought a complete upper when I built mine and had no problems. Also did the same for my 450 Bushmaster. You can make your brass from 223 or just buy some.

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I go even further. I have multiple 5.56 carbines and pistol but I also have built a 300 Blkout carbine, SBR and pistol. The carry cases for the different calibers are different (black for 5.56 and tan for 300 Blkout). I use magazines for my 300 Blkout that have rubber caliber ID bands (available on Ebay) on them and I NEVER take both calibers to the range at the same time. It only takes a second of distraction to load the wrong caliber into a mag and then the gun with disastrous results.

...opt for a suppressor if I feel it would improve things. Similar guns like my SKS don't bother me. But a guy was next to my wife and I at the range and he had shorty barrelled AR he was shooting 5.56 out of and the noise and blast was horrendous.

I'D LIKE TO THANK EVERYBODY HERE FOR THEIR GREAT ADVICE. I'M SUCKING IT ALL UP AND I'LL ROLL IT ALL AROUND IN MY HEAD, SO WHEN I'M READY TO GO, I'LL BE BETTER INFORMED.

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"He was kinda funny lookin'"

Several years ago a Class III dealer had a HK53 (I think that's the Model), 223 full auto 8" barrel with collapsing shoulder stock. He was test firing it into a dirt bank. He tried semi auto first: On the first shot, something punched him in the stomach so hard, he thought a bullet has hit a stone and came back into him! He looked for a wound, then any trace of an impact. Absolutely nothing, turned out to be the muzzel blast/concussion from being 10' from the back stop. At 10 yards no problem. A friend of my brother's owns that gun now, but I don't know if he got a suppressor for it.

Ivan

If I don't want to spend $800 on a suppressor I can do exactly the same thing with a .223/5.56. I reload, and I can make .223 subsonic to 3300 fps depending on how the gas/recoil system is set up. I can operate the bolt for the lower velocity rounds. There just doesn't seem to be any advantage to going .300 Blackout, though for the kind of shooting I do it wouldn't be a bad choice.

I have an SKS and a .300 BLKT almost dupiicates the size of the bullet so I would actually be somewhat redundant going with the .300.

Well, it was worth the consideration. I'm glad I got all of the inside dope so thanks again.

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"He was kinda funny lookin'"

By definition subsonic is speeds less than the speed of sound or less than 1150 fps.
Subsonic ammunition - Wikipedia
1150 fps is probably not going to have enough gas in a 5.56 to operate it.
I believe the BKO excels when using cast bullets as it is one of the few cartridges very compatible to the AR with cast.

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Front sight and squeeze

I built a 10.5" barreled 300BLK pistol that I sold to my BIL where he paid the tax for a suppressor. He is very happy shooting 168gr subsonic rounds in it.

I built my 300BLK about 8 years ago, built it as an M4, 16" barrel with carbine gas. I installed an adjustable gas block so I could control how much or little gas I needed, but leave it pretty much full open. I shoot mostly 125 and 155 loads, and use a H buffer and standard spring, M16 style carrier, no cycling issues at all. I share the lower for this rifle with a 6.5 Grendel upper, so I put a 2-stage trigger (Geissele HS National Match DMR) in it. I mostly plink with it at 100 and 200 yards, but have used it in a few CQB matches.

When reloading, you'll find that most powder loads that give you more than 1600 fps are compressed loads, if using AA1680. You may have to adjust your C.O.L. to as long as will feed from the magazine with the heavier bullets (150 grain and up). I use Lil'Gun, H110, and Win296 with good results, along with AA1680, which is the go-to for subs.

And absolutely, since you will also be shooting 5.56 in another rifle, mark your magazines clearly. A 300 BLK will chamber in a 5.56 rifle most times, especially with the smaller bullets like 110 and 125 grain. If you pull the trigger on one, it will be a short, exciting life for your rifle.

Attached Images

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In addition to my AR pistol in .300BLK, I have a Howa 'Miniaction' 1500.



While amazingly quiet with subs, the accuracy with UMC 220gr subsonic ammo wasn't impressing me. I took it to the range yesterday and shot some Frontier brand (cheap) 125gr FMJ supers and my concerns quickly evaporated.



I'm going to have to tinker with some subsonic handloads to see if I can get anywhere near the supersonic performance.

BTW, at 100yds, there's an 11.5" difference in impact point between the subs and supers.