The 300 Blackout is without doubt one of the most purpose-built cartridges within the AR world, designed from the bottom as much as carry out briefly barrels, run suppressed, and cycle reliably with each supersonic and subsonic masses.
However that versatility comes with a catch: barrel size issues extra with 300 BLK than with nearly every other AR caliber. Get it fallacious, and also you’re both leaving efficiency on the desk or preventing reliability points.
So what’s the optimum barrel size? The info factors to 10.5 inches, and right here’s why.
The Case for 10.5″
300 Blackout was particularly designed to be run in a shorter barrel whereas providing muzzle power comparable to five.56 NATO when that spherical is fired from a 16″-barreled rifle. When chambering supersonic masses, 300 BLK produces greater than 1,153 ft-lbs of power at 10.5″, whereas 5.56 NATO’s M193 load produces 1,161 ft-lbs in a 16″ barrel.
That’s the entire level of the cartridge, and 10.5″ is the place it delivers.
Reliability is the opposite half of the equation. The 300 Blackout spherical will get finicky if you swap out supersonic rounds for subsonics. A gun that is perhaps appropriately gassed for biking supers could wind up short-stroking or failing to cycle with subs.
However with a ten.5″ barrel, the subsonic spherical’s dwell time is ample to cycle the bolt with out the necessity for an adjustable gasoline block. At this barrel size, supersonic rounds don’t produce an excessive amount of felt recoil with a hard and fast gasoline block; the gun is neither over- nor under-gassed.
Should you’re operating each supersonic and subsonic masses, particularly suppressed, 10.5″ offers you the gasoline dwell time to cycle reliably with out including the complexity (and value) of an adjustable gasoline block.
What About Going Shorter?
A 7.5″ barrel doesn’t meet the definition of “optimum.” The supersonic load loses practically 20% of its muzzle velocity at that size, whereas the 190-grain subsonic load loses 10%.
Solely the heaviest subsonic masses (220-grain) strategy nominal velocity at 7.5″, dropping round 6.7%. You’re giving up an excessive amount of. The spherical was constructed for brief barrels, sure, however there’s a ground and seven.5″ drops beneath it.
Should you needed to go shorter than 10.5″ and are solely taking pictures subs, you may get away with an 8.5″ barrel size.
What About Going Longer?
At 16 inches, muzzle velocities are close to their peak. Supersonic ammo retains rifle-caliber velocities, has elevated efficient distance, and bullet drop is tremendously decreased. The 16″ barrel additionally delivers higher power on influence, no matter ammo sort. Heavy subsonic masses, nonetheless, can truly push into transonic territory from a 16″ barrel, which is the other of what you need when you’re operating a suppressor and making an attempt to remain listening to secure.
In case your use case is searching or general-purpose vary work with no suppressor, 16″ may make sense. However when you purchased 300 BLK since you need the suppressed subsonic expertise, a 16″ barrel is a no-go.
What About Twist Fee?
Barrel size is simply a part of the equation. A 1:8 twist works greatest with light-weight supersonic rounds. For these with suppressors, a 1:7 twist favors the heavier subsonic rounds. Should you’re constructing a do-everything pistol or SBR that may run each, 1:8 is a stable center floor; it handles most supersonic masses nicely and stays appropriate with many subsonic bullets, notably in barely longer barrels.
My Faxon 10.5″ 300 Blackout Construct
I needed a real brush gun, one thing brief sufficient to maneuver by means of the dense japanese woodlands of Northeast Ohio. When you consider a suppressor, a ten.5″ .300 BLK pistol retains the general size manageable with out giving up efficiency the best way a comparably brief 5.56 tends to.
The opposite consideration is bullet weight. Even lighter .300 BLK supers nonetheless outperform heavier 5.56 masses, and that additional mass tends to hold higher by means of mild brush and vegetation. In real-world searching situations, particularly in dense woods the place your sight image isn’t at all times good, that added forgiveness makes a distinction.
We ran a Faxon Sport 10.5″ 300 Blackout AR pistol paired with a Q Speakeasy suppressor and a C&H STRYKR purple dot.
For a brush gun within the japanese woodlands of northeast Ohio, I wanted an optic that would sustain with quick, close-range engagements in tight areas. The C&H STRYKR delivered. The multi-reticle configuration offers you a 3 MOA dot, a 33 MOA circle, or each mixed, and that circle-dot combo instantly jogged my memory of my EOTech 512. It’s a big, easy-to-acquire reticle that will get you on track quick.
At 3.68 ounces, it doesn’t add a lot to the general bundle, and the IPX7 waterproof ranking and absolutely enclosed emitter imply it’ll deal with regardless of the Ohio climate throws at it.
Utilizing HOP Munitions 190-grain REX and 220-grain OTM subs, plus 147-grain FMJ supersonic masses, this construct ran every part suppressed with no single malfunction.
No adjustable gasoline block. No buffer system tuning. It simply labored, straight out of the field. On the core is the Faxon Obligation Sequence Gunner Profile 10.5″ 300 BLK barrel, 1:8 twist, 4150 CMV metal, salt-bath nitrided for sturdiness and corrosion resistance, operating a pistol-length gasoline system.
Getting a 300 BLK construct to cycle reliably throughout each supersonic and subsonic masses, particularly suppressed, is one thing many shooters have struggled with. The truth that Faxon’s 10.5″ barrel is tuned nicely sufficient to make {that a} non-issue from the beginning is a real accomplishment.
Backside Line
For suppressed compact setups, a 9- to 10.5-inch barrel is the candy spot. For searching and basic vary use, 12 to 16 inches makes extra sense.
However if you’d like the one barrel size that greatest captures what 300 Blackout was designed to do, dependable suppressed operation with each supersonic and subsonic masses, in a compact platform, 10.5″ with a 1:8 twist is your reply.
And if you’d like that functionality with out the trouble of tuning your firearm, Faxon’s doing it proper.
