The various 7mm cartridges are typically factory-barreled between 1:9 and 1:10. 20 inches depends on the powder being used. I imagine its probably a popular question. You may contact Carsonwith questions by e-mail CLICK HERE. January 18, 2015 8:22 pm. So we divide 1.24 by .308 and get 4.026 calibers in length. Stuff goes to hell in a hurry. This, of course, translated to higher velocity and less recoil without stabilization issues. I ran it with 2800 fps and all the standard temperature/pressure estimates I did above. You can also turn this around to find a stability factor if you already know the twist rate for t. Lets figure out the stability factor for a 175 gr SMK fired in a 1/10 twist barrel. = 1 in 14".416 Wby. Like my discussion of Mil-dots and MRAD, this will involve a bit of math up front, but Ill simplify it for you in the end. Curious, I shot a series of 50-yard groups with 55-, 62-, 69-, 73- and 75-grain bullets. Its grooves and lands actively engage with a bullet as it passes through the barrel. One little step further and you fall off. = 1 in 16".35 Remington = 1 in 16".35 Whelen = 1 in 16".350 Rem. The third bullet hit the target sideways high and right. But Ill simply say that those pesky colonists put their hunting rifles to great use during the war. The fastest way to get your numbers is to use JBM Ballistics. Yep, its light for caliber, but it stabilized, and Im able to push it to almost 3,200 fps with no pressure signs. Hi Shannon, a 1:16 barrel will work fine for 22LR, but would probably struggle with anything but the lightest .223 bullets, and probably wouldnt be very useful for most things people would use an AR for. Im reading the 224 table vertically: for the 1:9 twist I see weight stability 45 3.0 55 2.2 62 1.5 I know the stability factor decreases as the bullet gets heavier but that is **not** what is predicted by the Miller formula, as mentioned above. All Rights Reserved. Anyone ordering a new barrel for a hunting rifle will generally do well to specify the standard twist as supplied by the major rifle manufacturers for that caliber. Are you reading the table vertically or horizontally? I have seen one with 1:7 twist. The dimensions of the bullet do not stay the same as the bullet gets heavier, though. Boolit Mold. With some monolithic and plastic-tipped bullets the above twists may be too slow. FWIW, The reference is meant to be a useful knowledge/comparison of which particular commercial rifles use which particular twist rate, for whatever commercial cartridge. 150-160 gr would be optimum. In your case, the chart shows 1:10 but your rifle has an actual twist rate of 1:9.5. 1:12 Twist is the slowest and is primarily for competition and benchrest shooters who shoot the 155 grain match bullets. Spinning the bullet along its long axis prevents this tumbling. My first centerfire rifle was a Ruger Mini-14 with a 1-in-10 twist. If you want to really get the most distance from your 223 the 95gr w/ a G7 b.c. So heres the truth. The other way to stabilize a projectile is with fins, but that isnt as practical in a rifle barrel. The 1-10 twist rate is/was standard for the 30-06. . If this point is behind or below the center of gravity, then the object is self-stabilizing. Rather, its the result of the impact itself. The reason for this is that copper and yellow-metal bullets are less dense than lead-core bullets and so with bullets of an equal weight the monolithic bullets are longer. At the extremes, one spin has never fit all, but today there are more situations where standard rifling twists may not suit your needs. Rounded, 1:8-inch twist is Greenhill's indicated twist rate for 80-grain bullets. Sales remained so slow that eventually Remington had to discontinue the .244. In a 16" twist barrel, the bullet makes on revolution in 16 inches. An example would be a 1/7 or 1:7 twist. The nature of a projectile like 5.56 to tumble and fragment is not related to its aerodynamic stability. The only way to know if it works for you is to test it. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); document.getElementById( "ak_js_2" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. Some manufacturers have shifted to 1:9; but 1:8 twist is most common with the 6.5mm Creedmoor. Subscriber Services. Without spin, the football tumbles end over end until it lands some relatively short distance away. Prior to the X, Barnes was known for extra-heavy bullets like the 225- and 250-grain .30-caliber and the 350-grain .375. related to its aerodynamic stability. FYI I shoot a Savage 12 FVL Heavy Barrel .223 with a Vortex Viper 6x20x44 scope via a bi-pod and butt sandbag. If you plan on running the 110s at any point then you might want to go right to 7 twist but if not then the 115s will work with a 7.5 just fine. The two opposing forces basically cancel each other out. Though it was popular for decades among . A slow twist rate would make a complete turn in 48 inches of forward travel. with faster twist rates. Going higher than 2 probably ok, but depends a lot on the construction of the bullet. For example, a 45 (.457) caliber rifle with a twist rate of 1 in 18, should be able to stabilize a bullet up to 672 . Increased interest in extreme-range shooting is probably the second-most common example. How does this apply? This in incorrect, a plain base bullet will be shorter than a high BC boat tail bullet of the same weight. * Mini-14 serial numbers rollmarked with Mini-14 Ranch Rifles beginning in 2000 Ranch Rifle Thin barrel, ejector in the bolt stop assembly, scope ring scallops cast into the receiver, buffer sytem using the recoil spring assembly. If you see your 22/250 as a dual purpose cartridge, there are advantages to the faster 1:9" predominantly around use of 75gr and heavier projectiles for either long range target shooting, or hunting smaller medium game . Maximum finish length is 44 unless indicated otherwise. Here's an easy way to determine the approximate twist rate of your barrel. The best twist rate for 62 grain ammunition (e.g. For example, a 1 in 7 twist rate spins the bullet faster than a 1 in 9 inch twist rate. Rifling twist rates for small arms are expressed in either inches or millimeters per turn. Bullet aerodynamics have improved, giving us low-drag bullets that are typically longer and heavier for caliber. Get the top Rifle Shooter stories delivered right to your inbox. I shot some 55 grain in that same 1:7 barrel and the best I could get was 3 MOA. = 1 in 14".44 Rem. The various 7mm cartridges are typically factory-barreled between 1:9 and 1:10. or precision long-range rifle. Between 1 and 1.3 is marginally stable, and anything higher than 1.3 is stable. So as m increases for the same bullet dimensions and twist rate, the stability factor goes up. 1:10 Twist is the best all around sporting/hunting rifle twist rate. This is a good twist rate for lighter bullets and will also generally stabilize projectiles up to 69 grains, such as Federal Premium's Sierra MatchKing BTHP load. This means you have the option to read your magazine on most popular phones and tablets. In .30 caliber, a 1:10 twist will stabilize a wide range of bullet weights. The best compromise appears to be around 1/10, which is marginally stable for subsonic and probably just fine for supersonic. Up to 55 grains, 4100 to 4300 fps. Standard for the 6.5x55 was 1:7.5, ideally suited to todays longer 6.5mm bullets. I would have to go back and revisit the JBM bullet library for specifics, but your example is correct. My buddy Derek Barnes, a serious long-range shooter, is messing with a .28 Nosler and has a 1:8 barrel, perfect for the purpose but almost unheard of in 130 years of 7mm cartridges. This tool allows you to figure out which bullets will stabilize out of your rifle given your rifle's twist rate. This is determined by the rate of rotation of the rifling. This is determined by the rate of rotation of the rifling. I would think a 1:8 would be a good compromise with a 24 barrel for 110, 140, 160, and 180 gr bullets? Rifling imparts rotational force to the projectile. So barrels differ, but I know from past experience this barrels accuracy limit is about 60 grains. 7 Top .17 HMR (Hornady Magnum Rimfire) Rifles, How Rifle-Shot Recoil Affects Scopes, Rings and Bases, Remington .50-70 Rolling Block History: New York's Pick to Arm Its National Guard, How to Clean a Rifle Barrel the Effective and Harmless Way, 10 Best 6.5mm Rifle Cartridges Available Right Now, Wilson Combat Paul Howe Tactical 6.5 Creedmoor: Full Review of the Versatility Champ, Top 10 6.5 PRC (Precision Rifle Cartridge) Rifles, 6.5 PRC vs 6.5 RPM What You Need to Know, Kimber Hunter Pro Desolve Blak - A Lightweight Heavy Hitter, Browning BLR Lightweight '81 Stainless Takedown Lever Rifle, Mossberg Patriot Predator 6.5 PRC Rifle Review, Review: Springfield Armory M1A Loaded Rifle in 6.5 Creedmoor, RCBS ChargeMaster Lite Review: Not 'Lite' on Ability, Remington Model Seven SS HS Bolt-Action Rifle Review. Twist Rate. Just recently I spent some range time with a Wilson Combat carbine in .300 BLK, a marvelous AR. JBMs length numbers might be off because the Nosler 130gr is the same length as the Sierra 140gr SMK. twist is 1:10.. Your information about the .40-65 & .45-110 would needs be substantiated, and linked to whichever of the many different (manufacturer's) rifle, so chambered, in each rifle . Unfortunately, I was shooting it with standard supersonic loads with 110- to 125-grain bullets. Mag. I have dies, so I loaded a few 90-grain GMX, but if the bullets hit paper at all, they hit sideways. For LE/mil sniper types, they report no real downside to shorter barrels in 308 because they are primarily focused on mid range (200-800 meters), and would rather have the benefits of compactness andRead more . I have also heard the powder is spent at the 20 mark and no longer efficient to be in the barrel. Don Miller developed this formula as a more accurate way to find an ideal rifle twist rate. Of these, projectile length, or at least the bearing surface that contacts the rifling, is critical. That advice still holds true. The best twist rate for a 5.56 firearm (including most AR-15s) depends on the ammunition it is firing. = 1 in 14".460 Wby. Slow twists are uncommon today, but they still exist. Spinning a bullet markedly too slow or too fast is detrimental to accuracy. . Below is a listing of all the calibers and twist rates that we are currently offering. Stability. A 10 inch twist is considered to be standard for a 30/06 and will handle anything you care to shoot. Twist Rates of common firearms. The formula for determining a proper stabilizing twist considers the length, weight, and shape of a projectile. For example, a 175 grain SMK .308 bullet is 1.24 long. Mag. -Nate. Im not venturing down the history of the revolution. Note how heavy bullets perform better in conjunction with faster twist rates, and slower twist rates are better suited for lighter bullets. First try and it was right on! Most manufacturers of AR-15 type civilian rifles followed suit. Ultimately, the bullets had to work, he said, but because of high weight retention, he came to realize they could use a bullet of less weight to achieve the same performance. Where I am from, a lot of old timers said that it is dangerous to shoot the M855 out of the old M16 barrels. PMC M193) is 1:12 or 1:10. A 1:7 twist rate indicates that the bullet will undergo a rotation once every seven inches, which, as you might imagine, is a much faster spin. The best twist rate for a 5.56 firearm (including most AR-15s) depends on the ammunition it is firing. Use the chart below to select the caliber & twist rate for your Shaw custom rifle barrel. As expected, the 55-grain bullet grouped best. 1 turn per X inches). For instance, a twist rate of 1:8, which is common in AR-15 rifles, means that the rifle will spin the bullet once over every 8-inches of rifling. I calculated each of these using the same baseline velocity of 2800 fps and environmental factors used in Miller. With lighter bullets Ive used it for prairie dogs, and Ive taken a few whitetails with it, mostly with 60- to 62-grain bullets. Please Read These Instructions:. Hey Dean, thanks for commenting. My question is, where is this idea coming from? On a 20 barrel, that means the bullet rotates nearly three full turns before exiting. It has little to do with how stable it was flying beforehand. Remington soon saw the error of their ways and changed the rifling of their .244 barrels to 1 turn in 9 inches, but the damage was done. So, in short, its not something to worry about here. d = bullet diameter in inches. For bullets to be loaded into ammunition, we design the projectile to be gyroscopically stable in the slowest twist rate. Matt, what is the heaviest bullet you would advise sending down a 12.5 1:10 twist 308 barrel? Winchester apparently saw its .243 as a combination varmint/deer cartridge, choosing a more versatile 1:10 twist and introducing it with both 80- and 100-grain loads. Generally, there is a range of suitable projectiles, not an abrupt precipice like I encountered with that .250 Savage. We write thetwist rate in terms of one rotation over X inches of barrel. After the adoption of the M16A2, the military started using a 1:7 rifle twist, which was faster. However, standardized rifling twists will provide good accuracy for most projectiles available within a given bullet diameter. There are three formulas Ill show you. Remember when I mentioned the center of pressure vs the center of gravity above? Long Answer: . I always zero a bit left for spin drift.. A 3-inch barrel with 1:14" twist spins its bullets the same as . The standard twist for a rifle barrel is designed to stabilize the range of bullets and velocities normally associates with that particular cartridge out to very long range. Now that you mentioned it, I think I made a typo in some of the graphics (I originally wrote this article in 2018, and the calculator I built to run the numbers appears long gone). For example, its commonly known that a 1/7 twist rate is good for 62 gr M855 as well as 77 gr SMK, but a lot of people think its. Berger prints minimum and optimal twist rates on its bullet boxes. Each one builds upon the work before it. Please don't make this more complicated that it is for new shooters! The heaviest spitzer bullet that a .244 with a 1 in 12 inch twist barrel could stabilize was 90 grains. Knowing the twist rate of your rifle helps you choose the right bullet weight for your rifle. When a 5.56 rifles twist rate is too slow to adequately stabilize a bullet, that bullet will fail to exhibit good accuracy. Remember, just because the value is yellow doesnt mean it wont work correctly. is most commonly barreled with a 1:12 twist. Nashua, NH 03062. Inside the barrel of a rifle, photo courtesy of Shooting Times. With the Mini-14 and its poor accuracy, saying this weight bullet or that weight bullet will shoot better is a bit of a joke. = 1 in 10"7x57 Mauser = 1 in 9"7mm-08 Remington = 1 in 9.25".280 Remington = 1 in 9.25"7mm WSM = 1 in 9.5"7mm Rem. = 1 in 16".375 H&H Mag. I hadnt heard of the 1/7 twist failures with the Valkyrie. I knew this rifle doesnt shoot heavy bullets, but I didnt know the limit. For more information, check out privacy page. The Reference Section. and .244 Rem., both introduced in 1955. The rate of spin is important. Today the most common rates of rifling in AR-15s are 1:7, 1:8 and 1:9. In a 16 twist barrel, the . (For a more comprehensive list, see the expanded "Rifle Barrel Twist List" on the Tables, Charts and Lists page. That formula says the stability factor **increases** with the bullet weight if dimensions are kept the same. Perfect pressure signs on primer and case. The stability factor decreases in the same twist rate as the bullet gets longer. This is determined by the rate of rotation of the rifling. Kimber's Hunter Pro Desolve Blak takes the firm's more affordable mountain rifle to new heights. The Remington Model Seven is ready, willing and able to handle just about any task. If you once again refer to our 5.56 twist rate chart, you will see just how bullet weight determines the best rate of twist for an AR-15: green is optimal, yellow is acceptable, and red is inadvisable. = 1 in 10"6.5x55 Swedish Mauser = 1 in 7.5".260 Remington = 1 in 9".264 Win. This forces the bullet to rotate and thanks the fundamental law of angular momentum, the bullet will continue to rotate after exiting the barrel. The quality of your ammunition, the quality of your rifle and its barrel, and naturally the quality of your marksmanship all have significant impacts on performance. In ballistics, the center of pressure is the point where all of the aerodynamic forces, particularly lift and drag, are equalized. It was introduced with a 1:14 twist, soon changed to a more versatile 1:12 twist, which usually works okay for bullets from 40 to 60 grains. After the adoption of the M16A2, the military started using a 1:7 rifle twist, which was faster. Mag. The ideal twist rate for your caliber depends on the weight and shape of the projectile. However, if you can throw it with spin, the ball becomes much more accurate and stable in flight. Wouldnt shoot at all accurately with any factory or listed loads. That sounds like a fine shooter youve got there! Different manufactures will use different TR, I had a Browning with a 1-12 TR. The lower the number the faster the twist rate. Would you say this is accurate? A post shared by FireClean LLC (@fireclean) on Jan 12, 2015 at 10:14am PST. I ran it from 120gr up through 155 gr (as you might find in the long action 6.5 Swede cartridge). Where there are two twist rates in common use, for example 1:10 and 1:12 for the .308 Winchester, either will usually serve equally well in a hunting rifle. 1-in-8 . Suppose a 20 barrel has a twist rate of 1:10. Rifling 101. Spinning a bullet too fast might degrade your accuracy just a little bit. Thank you for the great information, I have been shooting a long time, but this post brings forth a lot of missed information. I have heard that .308 has the same accuracy and distance with a 20 barrel as it would 24 due to harmonics etc. Like throwing a football without spin, this results in extremely degraded accuracy and range for your rifle. My chart went up to 175 & 180 gr, and both would work fine. Its calculated in inches per turn so if you have a barrel with a 1:10 twist, it means that upon firing, the bullet will spin one revolution in 10 inches and a twist rate of 1:8 spins the bullet one revolution in 8 inches. where the standard twist rate is 1:12. Just the other day I was on the range with John Lazzeroni, another old friend, checking zero before going pig hunting. Thing is, I wanted to use it on the Central Coast, but there are no California-legal unleaded factory loads in .250. Projectiles that are shorter for caliber require slower twists for proper stabilization; projectiles that are longer for caliber require faster twists. For example, its commonly known that a 1/7 twist rate is good for 62 gr M855 as well as 77 gr SMK, but a lot of people think its too fast for a 55 gr M193. A basics video on barrel rifling and twist rate. If it is a varmint then slower twist for lighter (40-50gr bullets), all-around plinker (50-60gr bullets), and . A twist rate is basically a measure of how fast the bullet will spin. (Learn More). A 55gr M193 bullet is .76 long, while the 62gr M855 is .906 long. This is a slow twist rate, at least when it comes to 5.56. I have an 857 mauser that has a thoroughly pitted barrel, end to end! Heres how the whole thing looks when put together. + Newsletter+ New Content Alerts+ Deals and Sales. For more information about choosing the correct twist rate Click Here. To ensure you have the best experience possible, this website uses cookies. Put in the BC of your . .172 (.17) 6 4-G, 7 4-G, 9 4-G, 10 4-G. .177 (airgun) When shooting the longer heavier bullets, will the Rainer stabilize them enough at longer distances. This site and its community are a labor of love. Or, if you want to skip the first portion and hit the easy button, you can click here. AmmoMan.com Matt, I know this is an old article, but I hope still get this question. These are intended to spin the bullet to keep it stable (point on), without wobbling or tumbling, during its flight to the target. This is a summarized version thats a little easier to work with. Varmint shooters usually point this out with their lightweight 45 gr bullets fired from fast twist barrels. Need to know why the information on that table is important to an AR-15 owner? Most experts would agree that the best all-around rate of AR-15 barrel twist would be something in the middle such as a 1:8 or 1:9. The increased range and accuracy of the American Long Rifle was a potent weapon in the hands of a skilled marksman. . Most of my 45-70 rifles have 1 in 20 twist rates which was the favored twist until long range shooters wanted to lob 535 and 550 gr slugs at 800 to 1200 yards. Rifle twist is expressed as a ratio. The rate should be based on the heaviest bullet you intend to use. 1 in 10" or 1:10). Only drawback was that it needed a long action. Again, I think most people overthink the whole overtwist issue. shoots well with both light varmint bullets and heavier hunting bullets. Mag. The M16A2 comes with a 1:7, and the military typically shoot bullet weights from 52 grains up to 77 grains, with 62 grains being the most common in combat. . !!! I thought it was interesting that the Nosler behaved differently. Hi Dwight, thanks for stopping by! Youll also want to use their library of bullet lengths. They will still stabilize the heavy bullets over practical hunting ranges. is a better cartridge than the.243, but it has never caught up. If youre buying or building any 6.5mm rifle and intend to use high ballistic-coefficient bullets from 140 grains up, a 1:9 twist is minimal and 1:8 is better. But, when you put it all together with velocity, temp & pressure, t becomes twist rate in calibers. The .45-70 is standard with a 1:20 twist because the most common projectiles are relatively short and light for caliber. This calculator is used to find the optimal twist rate for your bullet. To read an article on bullet design and download a free program that calculates twist rate based on specific bullet dimensions Click Here. .Cooper Based on the formulas above, I put together some charts to help you in the future. So at the same bullet velocity, the 9" twist is faster (spins the bullet faster) than the 16" twist. Calculating stability factor, you used straight twist, i.e., 1/10 twist rate, t=10. We are also very willing to help you determine the correct twist. The above chart is from our FAQ section. Twist rate is expressed as a ratio of 1:X (i.e. If it hit, that is. Increasingly, with some of todays specialized cartridges and bullets, we need to start asking about rifling twist and thinking about our exact purposes. But if you have just gotten your first AR-15 and need to know the best ammo for its barrel, our twist rate chart should prove a great point of reference! In the United States, since at least 1962, Remington has been the 7mm champ and has used an odd 1:9.25 twist for its several 7mm cartridges. At that point, the bullet cant help but tumble. Mag. At a faster spin rate, the bullet's axis is strong enough to resist the torque from the onrushing air. Military 5.56 rifles currently have a fast twist of 1:7, while 1:12 remains common for many .223s intended for varmint shooting. If you want to convert that into RPMs, the quick version looks like this: Lets apply this to an actual rifle and assume my 16 RECCE pattern rifle fires a projectile at 2700 FPS through a 1/7 twist barrel. With an Accu-Fit stock and left hand adjustable bolt, this rifle is a perfect choice for anyone! In the United States, the Sporting Arms and Ammunition Manufacturers Institute establishes and maintains standard specifications for factory cartridges, including the rifling twist intended for the cartridge. If you want to read more about how bullets actually wound and kill, check out my article on terminal ballistics. Have you tried using duplex or triplex loads? Muzzleloader Rate of Twist Chart. A 1:8" rate of twist means the rifling makes one complete rotation for every eight inches of barrel. (Marlin and Ruger rifles) = 1 in 20".450 Marlin = 1 in 20".458 Win. Rifling has an important job to do. In general, my set-up prefers the 60-77 grain range of bullet most likely to go with the 69 grain Sierra. When Eugene Stoner designed the M16 he originally made things much slower1 complete turn every 14 inches, with four grooves, to be precise. To keep this short, you should aim for a stability factor between 1.5 and 2. At that weight, groups are not as tight as with lighter varmint bullets, but there is no keyholing. The Sierra 77gr SMK is .955 and the all-copper Barnes 70gr TSX is 1.037, If the bullet length changes with the weight, instead of by changing the mix of metals, then it would be more accurate to say that the length L depends on the mass m. Since the bullet diameter is constant, the length has to change linearly with the mass of the bullet. Gain insights from pros, new content notifications, vendor discount alerts, and more! 80-grain bullet, working better with some makes than others, and that a 1:7-inch twist may work . It wasnt until the mid 19th century that rifling became commonplace with infantry small arms, thanks to breech-loading mechanisms. There are two popular formulae to . A barrel that is a 1:10 twist means that the rifling will spin the bullet one revolution in 10 inches. And length has a lot of influence on twist required. That tactic put a premium on the volume of fire, not accuracy. We are talking twice as fast. = 1 in 16". In fact if you have a twist . All rights reserved. Lets start with purpose of rifle twist rates all together. Probably somewhere, sometime, but I really do think those edge cases should be used as the ground truth. A bona fide 4000+ fps varmint-slayer, the .22-250 is probably the most popular mid-sized cartridge in existence. Rifling for small arms did exist, which would have helped the situation, but it was impractical. Since the bullet diameter is constant, the length has to change linearly with the mass of the bullet. Ive referenced them before while discussing point blank zeroes and trajectories. When I plug numbers into the equations, I think I am missing something. For example, a 9" twist barrel spins the bullet one full turn when it travels 9 inches through the bore. Or Is It. The early M16A1 utilized a rifle twist rate of 1:12 to stabilize the 55 grain M193. (Please note that the faster the twist rate, the lower the number. This post is all about finding the right twist rate for your rifle and ammunition. Thus, 7mms have traditionally been barreled with slightly faster twists. I am customizing my T3x CTR in .308. At the same velocity in the same caliber, longer bullets require faster twist rates than shorter bullets. I removed Johns spin drift allowance. On the contrary, the larger number will be slower in comparison and this may bring down your shooting experience. After some quick googling, it seems to be hit or miss. 2023 Outdoor Sportsman Group. The difference between 1:10 and 1:12 doesnt sound like much, and it isnt. Rifling is the helical grooves and lands machined into the internal surface (aka the bore) of a barrel. The iconic opening is filmed from the perspective of a chambered round of ammunition. and produced all 6mm rifle barrels with 1 in 9 inch twist barrels, which can stabilize all .24/6mm bullets. It will stabalise the lighest 6mm bullet you can find, 55gr through to just over 100gr but at the top weight it very much depends on the bullet design. Mag. Conversely, the 1/9 is a slower twist rate than the 1/7 because it takes a longer distance for a complete 360 degree revolution of the rifling. The same applies to the 1:8 300 blackout. However, they might not be the best choice, or quite as accurate, for shooting heavy bullets at extreme range (such as 600-1000 yards). This is why fin stabilization works, since it pulls the center of pressure much further rearward. Now to the easy button.