Asking people who have real world experience, what can you expect? I’m thinking about a 7 inch barrel, BCM to be exact. I will be shooting factory ammo for now. I realize that in my hands there are lots of factors, distance, optics, and how much caffeine I have had that day lol. Just curious what others have achieved, and what I should expect!

Accuracy depends on barrel and ammo quality. If you get a good barrel and shoot good ammo, you will have good accuracy, as a general rule.

I'm not an expert, but I think you need at least 9 inches to stabilize .300 BLK at sub speeds. My suppressed MCX is quite accurate at range distances, preforming as accurately as my 516. This is not so with the 7 inch upper on the 516.

From my experience, I would recommend 9-11 inches if it were me.

H&K-Guy

How long is the barrel on your MCX?

quote:

Originally posted by pepsiblue:
How long is the barrel on your MCX?

9 inches

H&K-Guy

I have an 8.5" SBR in 300 blk with a Rainier Arms barrel. Honestly I'm unsure as to what barrel line it was as I bought it 9 years ago at this point.

I don't do much shooting over 50 yards with it, however last year I did take my shot at 275 yards while sitting on the ground. I have a Trijicon MRO on it so I have no magnification. I shot at an 11x18 target 5 times and had hits on 3 out of 5. I am quite confident with some magnification I would be able to put together a solid group. This is a sample size of 1 on a homebuilt rifle and 150gr reloads.

I run a 10.5" 300 BLK pistol with a a hand guard that stops just short of of the muzzle threads. Performance of supers and subs are just about right with a long enough hand guard to fit my big ole mitt. I also run a RARR bolt gun and really can get some distance out 125-130 gr supers. Last outing with the rifle put 125 TNT's into about 4" at 400 yards...in a windy as heck morning. Once in awhile things kinda come together...and I spent a few years sorting out what the little case can do for me.

pepsi,

Again, I'm no expert, but I'm just curious. What are you going to use your .300 BLK rifle for? The reason why I ask is that one of the main reasons why you would choose the .300 BLK round is to suppress.

If you are shooting 200-220 grn subs, you need a different pistol/SBR than if you are going to be shooting 160 grn supers. Barrel length, twist rate, and your ammo choice are factors you want to consider.

I highly recommend you go with an adjustable gas system if you want to run the gambit.

So what are you going to do with this pistol/SBR? What parts are you considering? Tell us more.

H&K-Guy

quote:

Originally posted by H&K-Guy:
pepsi,

Again, I'm no expert, but I'm just curious. What are you going to use your .300 BLK rifle for? The reason why I ask is that one of the main reasons why you would choose the .300 BLK round is to suppress.

If you are shooting 200-220 grn subs, you need a different pistol/SBR than if you are going to be shooting 160 grn supers. Barrel length, twist rate, and your ammo choice are factors you want to consider.

I highly recommend you go with an adjustable gas system if you want to run the gambit.

So what are you going to do with this pistol/SBR? What parts are you considering? Tell us more.

H&K-Guy

I would beg the differ on this post. My 300blk uses a 8.3” Ballistic Advantage Hanson barrel. I load 110gr, 125gr and 220gr subs. It stabilizes all of them and shoots 1 - 1.25” groups at 100yds. It is also nice and quiet using a 9mm can for the 220gr subs. I use it to hunt hogs and it is a beast in that role. It took 3 last year .

usncorpsman, that is a sexy beast you got there. Meaning the .300 BLK, not the hog. Looks like a Luepold scope mounted on top?

I currently have an MPX with the 8 inch barrel. I love it, and I really have no complaints with it. I like the 30 round capacity, the small size, and the fact that it folds up. I can drop it in a gym bag, or in a backpack, and it’s good to go. Even with a few extra magazines, it’s still a small easily transported package.

A couple days ago I was listening to a podcast by Trex Arms, about the the Grey Man ideology. One of the things talked about was concealing your weapon, and the advantages of PCC and AR pistols with a brace. A 300 with a 7-8” barrel, and a Law folder will have about the same footprint as the MPX. The 300 would definitely have the advantage as far as power, and definitely an advantage as far as range goes.

Maybe I just need an excuse to get a new gun, but it definitely got me thinking!

A 300blk using subsonic ammo probably has similar muzzle energy to your MPX. Depending on the 9mm ammo you use in the MPX, it might have greater muzzle energy than a subsonic 300blk load. Supersonic 300blk loads from reasonable length barrels produce true rifle muzzle energies -- possibly 2.5x (or more) the ME of a pistol carbine round.

As mentioned above, and with other rifles, the accuracy of 300blk systems varies. My personal experience is with a factory Wilson Combat AR15 upper with an 11.3" barrel, 1:7 twist. Based on information shared with other precision shooting buddies with 300blk uppers, my experience seems similar to theirs. All my ammo was shot suppressed.

I find accuracy with subsonic ammo quite disappointing at any distances beyond 25 yards. Lateral variation is minimal and windage isn't much of a concern at shorter distances. But the vertical variation in bullet impacts is quite poor. I tried Sellier & Bellot 200 FMJ, Hornady 190 Sub-X, and Hornady 208 Amax. I saw no reason to test further. 2-4 MOA verticals are what I experienced. The rounds drop like a rock at distance, even 100 yards.

FMJ ammo with 123-150 grain bullets showed poor accuracy, regardless of brand. I got a couple of 1.5 MOA 5-round groups here and there, but most were in the 2-4 MOA range.

Accurate loads boiled down to those with 110 grain Vmax, 110 grain Barnes, and 125 HPBT bullets. I tested accuracy at 100, 250, and 370 yards. Hornady 110 VMax ammo produced some groups under 1 MOA, the majority a little over 1 MOA, and an occasional WTF flyer group of around 2 MOA.

The most consistent ammo by far in my barrel is Aussie Outback's 125 SMK. Even in high winds I could keep vertical variation below 1.1-1.2 MOA out to 445 yards. Came up with a few .8" groups at 100 yards.

My barrel's chamber appears to be pretty tight, and some of the hotter factory loads didn't play well. Both Fiocchi 125 SST and Sig 125 HPBT were accurate loads, but they popped primers repeatedly and jammed the gun. Records show that I tested 20 difference types of factory ammo in my 300blk upper.

The appeal of 300blk depends on your end use. I bought the Wilson upper to start my SBR journey. I chose the 11" barrel on ballistics, for close training on AR500 steel targets. I wanted to use supersonic FMJ loads of 140-150 grains, and keep the muzzle velocity below 2100 fps, so I didn't ding up my steel targets. Turns out that most 125 grain factory loads are around this MV, so I'm good to go with training options.

My MCX with 6.5in barrel shoots subs and supers under an inch out to 75 yards, thats as far as I've tested it as I was running low on factory 110gr Barnes. The subsonics was Sig 220gr. I'll be handloading my own 220's shortly as well and some other 110gr loads and will get it out to distance. So far it shows promise with my limited testing.

This message has been edited. Last edited by: WARPIG602,

I found much the same thing as fritz in my testing. 110, 125 bthp were my best performers for supers. 123, 124, (7.62x39 bullets) were shit. 140-150 grain bullets (308) were complete shit. 200,210,220 grain subsonic bullets were almost as accurate as the supers.

My average using my scope was between .9 moa and 1.5 moa. Which is fine for what it is. They were pretty consistent out to 100 yards. I have not had much chance to try it out past that.

What is the best all around preferred rifle twist rate for 300 BlackOut SBR or pistol AR15 plateform -barrel lengths 7.5 to 10 inches shooting 110 grain to 220 grain? Looking for something with good accuracy out pass 350 yards with both supersonic and subsonic(suppressor use) ammo.

With the prices or availability of 300 BO ammo these days I just don't want to waste my time and money to find my ammo are key holeing at longer ranges. This will be my backpack/truck gun.

My Black out originally had a Odin Works 16" barrel and shot one of my handloads very well. The bug bit me and I changed to a SBR and F1 supressor. The barrel is now a 10 1/2" 1-8 twist Odin Works barrel and it shoots the same load just fine. Here is a 100yd target from last winter.

Don't hammer me on the 3 shot group.It shot just as I expected. I was just verifying zero before a late season doe hunt. The load is 125gr Sierra Pro Hunter over near max load of H110.
To answer OP's question, barrel length shouldn't affect accuracy much in a BO.
I share Fritz's frustration on subsonic accuracy. I cast my own subsonic bullets and it has been a challenge. The quest continues.

I've had four "300 blackout" pistols, they were all good for around 1 MAO, one would do a bit under an inch at 100. But they all looked like this.



All with different names, I've had 4 contender pistols, one contender rifle, one bolt action rifle and 3-4 AR's and none of them impressed me accuracy wise. The best of them were the pistols, only just sub 1" groups at 100 yards. (compared to other calibers I have that will do 1/2" easy, even 1/4" groups at times)