300 Blackout vs 308 Caliber Comparison: Why Intended Purpose Matters

The 300BLK is designed for a full burn of powder in a 9" barrel. But IMO it’s really designed for the reloader, esp’ if you want to shoot subsonic loads. I don’t have huge experience with factory ammo but the 2 loads I did try (both S&B since that’s all I could find) one was a supersonic 110 and that functioned fine, the other 200gr load didn’t function my gun. As I wrote I didn’t try a bunch of different factory loads. After the S&B experience I just decided to make my own and tailor them to the gun. Today there might be 10 different loads on the shelf at the LGS.

If you want a short barreled gun that is precisely what the 300BLK is all about… decent performance out of a short barrel. The same barrel length chambered for other cartridges have lots of downside to them. As Festus wrote flash is one and I’m sure someone else wrote, blast being another.

Is it a 1000yd sniper cartridge? No but to wasn’t designed to be. It’s for CQB, exactly what you’re designing the gun for. But it will also be useable out to 200 yards with the right ammo. For backpack use it can be designed with a joint in the buffer tube. Heck, there are also QD barrel systems, but you’d need to research them for yourself. My point is that your backpack gun can be made small enough that no one would ever suspect “that small pack” could possibly contain what it does.

Accuracy? Without trying, my first test loads with Maker85s for HD all had 50 yard groups under an inch with my old eyes and a red dot sight. Everything else being equal that’s 2" at 100 yards. And that’s out of a light firearm. Not too shabby. Yeah, that’s better than most factory 7.62 x 39 ammo will do, so I’m told. I don’t shoot it. But since that load is for in house even 50 yard accuracy is a moot point. It’s sorta difficult to justify deadly force at 50 yards or further unless society completely collapses. FWIW, I would have accepted 3" at 50 yards and had absolutely no idea what to expect. I was tickled.

Recoil is not an issue. It’s been decades since I fired any 7.62 x 39, but I remember it having more. If I need to remove the arm brace from mine I would have no problem cheeking the buffer tube or even putting the buffer tube against my shoulder (or I could SBR it). It has slightly more recoil than a .223 or 5.56, but it’s also a lighter gun. How much? I’m terrible at judging recoil. To me unless something has huge recoil it’s a mousegun.

My source for 300BLK info is 300BLKtalk.com


I would do the short barrel upper in 300bo and the reasons have been stated by the others above. It will not be cheaper to shoot and buy ammo but, the reliability of this combo lower with 2 uppers that are reliable will be worth it.


I like that his advice was not just to fire the double-barreled shotgun out the window, but also to fire both barrels so it is empty.


Bet that’s the exact tactic that all of his Secret Service guys are taught to use too…:man_facepalming:t2:


I weep for my wallet. But it’s got to work when I need it to. 300 BLK it is.


I did a 300BO build, think it reached 2k

tons of fun though!


I like it. It just needs a light/laser.


Much better than 300 whisper rebranded by that dipshit Silvers. He actually said the penetration at 10 meters and 300 is the same. He is fake news, before Trump used the term to describe bullshit artists.

6.8 is a great all around cartridge, and 5.56 replacement.


Just do it right otherwise it’s $ wasted and that’s REALLY expensive!

I’d spend some time on 300BlkTalk -Index page
researching the build. I suggest you don’t build a firearm that needs tuning to run. That means you want a pistol gas port and a 9-10" barrel (think 10" for some dwell time). A standard weight BCG and carbine buffer is also good. I used a 10.3" Ballistic Advantage barrel and it’s fine. I didn’t scrimp on the BCG and bolt and since a can is attached I used a JP Enterprises for it’s wipe clean “super surface” that doesn’t even require lube. I lube it anyway. My buffer is a standard weight and it works fine with the proper ammo. All of it is your choice, but the rest that I won’t mention definitely is. That’s what’s nice about the AR, it’s LEGO. When I built mine I had definite ideas about what I wanted after decades of using other folks ideas of what I wanted. I can run mine, scratch that. Correction: I must run mine with either a can attached or any muzzle device attached to get the blast beyond the carbon fiber handguard. But I really don’t like short handguards, so the longer handguard was a must for me. But with either the linear comp or the can in place it runs the same. The can is there to absorb the blast. It does mitigate the sound somewhat but it’s biggest claim to fame is that it only makes the firearm 4" longer while doing the job of removing the blast effect for cqb. Fire a bottleneck cartridge indoors and you will immediately experience what the can (Amtac CQB) removes. Be ready for pain and potential ear drum damage if you do that. That was a warning. Of course all cans do the same job, but not all cans are as short as the Amtac CQB and I wanted short at the expense of hearing. Everything is a tradeoff. I hope I never use it w/o hearing protection, but if I do I’ll never hear the shot and I’ll deal with it if I survive.

Pay attention to magazines. Supposedly the cartridge works with 5.56 mags, except the internal ribs are different for 5.56 compared to what works best with 300BLK. Also, there is a huge difference with mag springs. 300BLK has much heavier bullets and needs more powerful springs. I bit the bullet also and while I wanted to use my 5.56 mags I dug into my wallet and bought 300BLK specific mags. That was a bite in the butt. Maybe 5.56 mags will work but I didn’t want to chance it. My 300BLK needs to work 100% too. What’s our lives worth? I think more than a few hundred dollars. I think I bought Lancer 300BLK specific mags and they work flawlessly.

Here’s mine with the linear comp in place. With the reflex can for HD it’s not much different. Right now it’s a handgun, but a few dollars for a tax stamp and a stock turns it into a SBR. I still might go the SBR route with it.

With the everyday can in place. Look closely at the vent slots and the reflex can can be seen under the handguard running back over the barrel.

And with an end of barrel can in place. 4" of the can is actually hidden by the handguard. That suppressor can also only be used with subsonic ammo. It’s an old pic, that arm brace has long since been removed. I hated the additional weight.

I like the reflex can so much more if I ever need to use it for HD.