It doesn't make any difference, your results on target are not dependent on the twist rate, and load data is the same regardless. You have to understand - that fast twist is there to handle heavy bullets for subsonic loads. There is no "optimum" supersonic bullet weight for those fast twist barrels, because the optimum weight/length is about double what you use in a supersonic load. Here is the old barrel length again… Longer barrels have been proven to have better velocities and it depends on your burn rate on your powder whether you get the full use of your barrel.
The AAC uses a similar weight and dimensional bullet as a 30BR and 20 inch barrels and longer are the standard for those highly accurate bolt guns. A 30BR pushes from 107 grains to 120 grain 30 cal projectiles. The 30 BR is expected to shoot sub .5 MOA out to 300 meters and weight is at a premium for most of these guns. A lighter gun via barrel would allow more other things to be used.
But shortening the guns usually has resulted in less accuracy. Determining proper twist is a factor of bore diameter, velocity, bullet weight and even bullet construction. That did more to spark interest in NFA items than anything. And adding a foot-long can to a full-length rifle is not optimal, particularly when you can push a 220 grain bullet to just under the speed of sound in six inches or so. Its not going to be long until you want to suppress it and/or SBR it. If you start with wanting a suppressed gun, you will eventually get to the 300.
Since the paperwork and tax didn't kill you, and they already have your fingerprints, you're gonna want to SBR it. Any time you put a can on a rifle, an adjustable gas block will allow you to tune it. I came here for a clue about what barrel to get for a pistol build, but I know once I have it I'm going to want a real stock and a suppressor. The 10" has a pistol length gas system, the 16" has a carbine length gas system.
I believe the port on the carbine length is sized differently . My understanding is adjustable gas blocks may be necessary when using different powders with subs. Of course I also had to work up the load so that they would operate the bolt and lock back, in addition to accuracy testing, but all factory loads operated both uppers, no problem. You can do a web search to find out what size gas port you need for your gas system length, different manufacturers use different sizes. Terminal performance testing on over 2000 Texas feral hogs and various game animals as large as 800 pounds has proven it to kill much more effectively than the 6.5 Grendel, 6.8 SPC, 7.62×39 or 300 Blackout.
Due to the optimization of bullet weight to barrel twist, accuracy has proven to be outstanding. Sub one-inch groups are the norm with multiple bullet choices for varying applications such as hunting, target shooting and tactical use. You're unlikely to find a 1-in-14 barrel on any AR-15 produced in recent years, but they do exist and you may encounter them on a bolt action rifle on occasion. This is the least-versatile twist rate you'll see in the 5.56x45mm/.223 Remington chambering.
Although 1-in-14 barrels can stabilize 55-grain bullets used by the original M16, it's really better suited for bullets up to 50- and 52-grains—most of which fall into the varmint and target category. If achieving maximum velocity with light bullets is your goal, this may fit your needs — Winchester's 45-grain JHP load is a screamer at 3,600 feet per second. This is the beginning of the road for the shooter wanting to take advantage of the heavy bullet trend.
The 1-in-9 is a great compromise twist rate—not too fast to cause problems with the 55-grain bullets, but fast enough to stabilize all but the heaviest bullets under most circumstances. This twist will stabilize most traditional bullets up to 75 grains, and monolithics up to 70 grains — but they do so right at the edge of the envelope so not all rifles will do it. With longer barrels and commensurate faster velocities, this twist can be more forgiving. The second side of the .300 Blackout's personality is subsonic. Typically, subsonic loads feature heavy bullets-200 grains and heavier-loaded to velocities below 1,080 fps. These loads are not as effective for hunting, as the bullets generally do not expand.
Some rely on heavy bullets to tumble upon impact, but that is not reliable and should not be counted on for consistent terminal performance. The trajectory of subsonic loads is also very difficult to shoot accurately at longer ranges without a lot of practice. For hunting, it's best to stick to the 110 or 150-grain selections. When choosing between 300 Blackout 1-8 or 1-7 twist rates, consider over-stabilization. This usually happens when you shoot a bullet through a gun barrel with a faster twist rate than what's required for the particular bullet weight.
HPR Ammunition designed this ammunition for hunters to achieve consistent sub-MOA accuracy. Loaded with the Barnes TAC-TX bullet, this load was the most accurate out of all 17 other types of ammo in this test. What makes HPR's load more accurate than the others with the TAC-TX bullet?
The most likely answer is that this ammo simply performed better through our test barrel. A different barrel could have showed completely different results. Among the TAC-TX loads tested, HPR recorded the lowest standard deviation of velocities, which accounts for consistent powder burns, case pressures and bullet seating. Well, an obvious difference was the barrel; a full 5.5″ shorter than the others. The oblong bullet holes indicated bullet yaw related to the rifling. It appeared the twist wasn't quick enough to fully stabilize the heavy bullets when fired at slower pistol velocities.
I declared a cease-fire to avoid the possibility of a catastrophic baffle-strike in the suppressor and looked for a lighter bullet. I currently own two AR-15s with 1-in-7 twist rates — a 10.3-inch Mk18 Mod. To illustrate how velocity and twist rates can be the ying and the yang of bullet stability and accuracy, I fired a variety of loads side-by-side from the two rifles.
When the U.S. military first adopted the M16 rifle in the 1960s, the M193 cartridge and its 55-grain bullet was standard. The earliest issued variations of Eugene Stoner's "Black Rifle" came with relatively slow rifling twist rates of 1-in-14 inches. Shortly thereafter, nearly all M16s and M16A1s were being issued with faster 1-in-12-inch twist barrels. The .300 Blackout has two very different personalities, the first being supersonic bullets.
The .300 Blackout is capable of driving bullets up to 150 grains in excess of 2,000 fps, which is more than enough velocity to get reliable expansion at moderate distances. Generally, the .300 Blackout is loaded with 110- to 125-grain bullets for hunting. Velocities range from 2,200 to 2,350 fps, combined with the bullet weight and expansion characteristics delivering a very effective performance on game up to and including mule deer. A big advantage to the .300 Blackout is that it allows a user to use only one caliber while switching between barrier penetrating, subsonic, and supersonic ammunition all the same time. Based on the chart, if you plan to use a heavier bullet, choose a faster twist rate to ensure stability.
Generally, you can still shoot through 300 Blackout barrels with a twist rate that's at the end of another fence, but it won't ideally give you the maximum ammunition performance. A 10-inch barrel on an AR pistol or a short barreled rifle is perfect for the .300 Blackout. The uppers all feature different length handguards, that accommodate the mounted flash suppressor.
The barrels are all equipped with a standard A2 muzzle brake that's been proven efficient and effective. That may affect accuracy, although probably only minimally. It's a good idea to use ammunition with the ideal range of weight grains with the following range of barrel twist rates.
This will help maximize the stability of the round and the accuracy of your shot. Having a longer or shorter barrel is a matter of understanding the dynamics of ammunition, barrel design, and overall shooting conditions before you settle on a preference. For instance, having a relatively long barrel has the gases from the already burned-out gunpowder trapped for longer, which means there will be more push time of the bullet by the gases. The shorter a gun barrel, the more the gas expulsion at the muzzle equals a relatively louder sound every time you shoot. To counter this, of course, there is always the option of sticking a silencer onto the muzzle. In instances where that is not an option, however, you can always go long or brace yourself for those loud blasts with every shot.
The 220 grain subsonic .300 Blackout goes at about 1010 feet per second with 500 foot-pounds of muzzle energy. This makes the .300 Blackout an effective, versatile, and reliable close combat round. The .300 Blackout also comes in a supersonic variant, which means once fired, the bullet travels faster than the sound barrier. This high-speed feature means that the bullet will spend relatively less time in motion and thus less prone to the effects of elements like the wind. Aluminum is much lighter than copper or lead, which is why this bullet only weighs 78 grains versus 115 grains for most supersonic 300 Blackout bullets. Due to the bullet's light weight, it's able to reach a muzzle velocity of 2,800 fps—almost as fast as a 5.56 and much faster than standard 300 Blackout ammo.
Matching the rifling twist in your rifle or carbine to the appropriate ammunition won't guarantee great accuracy, but it will ensure the bullet is properly stabilized in flight. On the other hand, using a bullet that's too heavy for your barrel's twist is a virtual promise of poor accuracy and ineffective terminal performance. If you're struggling with the accuracy of your modern sporting rifle, be sure you've properly matched your ammunition to the barrel's twist.
Our .300 BLK barrels are designed to perform with both subsonic and supersonic loads. The gas port has been tuned to lock the bolt open on the last round when using subsonic ammunition with a sound suppressor or supersonic ammo without a suppressor. The bolt may not lock back when using subsonic ammunition WITHOUT a sound suppressor installed. Please note that subsonic ammunition can be more prone to malfunction than supersonic ammunition. If you are looking for a short pistol length barrel for your .300 Blackout AR-15, you'll want to take a close look at the Palmetto State Armory 10.5" CHF .300 Blackout pistol gas barrel.
This barrel is hammer forged out of chrome moly vanadium steel and is also chrome lined on the inside of the barrel in order to extend its overall service life. The chrome lined barrel is considered to be military standard for this same reason. I have a bunch of lower AR receivers on the shelf I can build on and have contemplated building a 50 Beowulf or 450 Bushmaster rifle. I've shot 50 Beowulf full auto and it is quite the experience. The projectiles used in subsonic .300 AAC Blackout loads usually weigh between 180- and 220-grains. Gemtech, widely known for their lineup of quality sound suppressors, is now producing supersonic and subsonic .300 Blackout ammo as well.
Their supersonic variety is loaded with Barnes' TAC-TX bullet on factory-new Blackout brass, not re-sized 5.56 cases. Gemtech advertises this load to be effective for helicopter hog hunting, which is certainly possible with its average velocity of 2,212 fps through a 10.5-inch barrel. Loaded with their all-copper TAC-TX bullet, Barnes has designed what is, in my opinion, the best all-around commercially available .300 Blackout load on the market. The 110-grain polymer-tipped copper bullet is precisely seated into factory-new Remington brass at an overall length of 2.25 inches for reliable feeding with standard AR mags.
Four razor-sharp petals are purposely designed to peel back at a lower-velocity expansion threshold near 1,400 feet-per-second . This results in full expansion out to 300 yards when fired through even short barrels.Read the full review here. Again, how you plan to use your AR will play a part in how long a barrel you choose. A longer barrel will allow the expanding gas behind the round to build to a greater pressure, which will increase muzzle velocity, and all the rifling will further stabilize the bullet. Then one day I was corresponding with Ron Reiber of Hodgdon Powder Company and he strongly suggested that we try their new CFEBLK powder.
To make this long story shorter, this ended up being a game changer and the final piece to the puzzle. It gave us improved accuracy and more velocity with less pressure allowing me to exceed my original velocity goals. Once I decided on a 1-15 twist rate for the barrels and we were good on ballistic performance and accuracy, all that was left was to decide on a name and test real world terminal performance. The length of a barrel also dictates the rifle's twist rate and thus the bullet as it travels down the barrel. The twist rate is when the bullet twists within a barrel once fired, which helps keep it at a high velocity and helps maintain accuracy. A longer barrel has a slower twist rate and provides more power and accuracy, which is better for long-range targets.
A longer barrel, because of its increased surface area, provides more room for cooling in instances where you shoot continuously. This is the slowest twist still seen in large numbers on AR-15s and other .223s. Though far better than the 1-in-14 twist, it is still unsuited for some of the premium loads developed over the past decade. Conventional wisdom suggests this twist rate is perfect for bullets in the 55-to 60-grain range, though most will stabilize the common 62-grain FMJ rounds. If you hunt prairie dogs or coyotes with lightweight .223 bullets, this twist rate will do fine for your needs. Doubletap's 55-grain Nosler Ballistic Tip load generates 3,300 feet per second of velocity out of a 22-inch barrel, and will easily stabilize in this twist rate.
When it comes to twist rate accuracy, there is no "one size fits all" concept. There is no all-inclusive twist that will work for any of your cartridges or any single cartridge in the market, for that matter. To be accurate, twist rates need to match the components of the bullet you're firing.
In determining twist rates, the bullet weight's role is more of a correlation. A significant factor in choosing the right twist rate boils down to the length of the bullets. The reason weight comes into the picture is because the longer the bullet, the heavier it will be. And the heavier it is, the faster the twister rate you'll need to reach stability in that round in flight. The 300 blackout is basically designed for military use as an assault rifle with the M4 as its original platform.
H&K MP5 SSD sub-machine gun, the outcome is a short barreled AR rifle type that can fire full auto 9mm even with a suppressed barrel. In the purpose of the .300 AAC Blackout cartridge, subsonic loads are great for target shooting and home defense or tactical applications where stealth is mission critical. On the current market of factory-loaded .300 Blackout ammo, FMJ offerings are sparsely available amongst all the other cartridges specifically designed for hunting or tactical scenarios. One reason why is because most people who reload the cartridge will have no problem finding .30-caliber FMJ bullets for a bargain, and make their own loads. HPR Ammunitionsatisfies the need for an everyday practice and plinking variety with their 110-grain FMJ. To get a brand new scope zeroed in for supersonic .300 Blackout, start with this ammo to get on paper and then fine-tune your zero with the specialty ammo of your choice.
The first rounds through my pistol-length .300 Blackout AR-15 offered promise. Off shooting sandbags from 100 yards, five 110-grain supersonic handloads formed a tidy 1.25″ cluster. So far so good, but my main interest involved subsonic loads for use with a suppressor.
When projectiles are launched below the speed of sound, the telltale supersonic crack can be eliminated for truly quiet shooting. That slight twist made the arrows spin after they were released from the bow. German gunsmiths applied the same concept to their barrels by cutting twisting grooves in the barrel. This twist helps stabilize the bullet in its trajectory, making the weapon more accurate at a longer distance.
