rifle twist rate chart

For this article, I shot a 50-yard test group with the 55-grain V-Max, all shots touching. Mag. But the length of the bullet does change as the mass increases. They also think its excessively fast for a lighter 45 gr varmint bullet. A slow burning powder will need a longer barrel to burn up. This means you have the option to read your magazine on most popular phones and tablets. By then the .243 had caught on, while the .244 never would. 7mm bullets tend to be longer for caliber than .30 caliber bullets. Your mileage may vary, of course, depending on your experiences. I also provided a few links to online calculators that do a great job. Would you say this is accurate? In developing the Barnes X, Randy told me that he had to constantly consider rifling twists because a copper bullet is longer than a lead core bullet of the same weight. Not sure how the tables for 224 stability follow from the Miller formula: that formula shows that the stability factor **increases linearly ** with mass m of the bullet, but the tables show it decreasing non-linearly. Since it cannot increase in diameter (it always has to be .224), then the bullet must increase in length to accommodate the extra mass. The correct rate of twist is . I also have an older AR with 1:12 twist. Different bullets utilize different twist rates to maximize stability and accuracy. (For a more comprehensive list, see the expanded "Rifle Barrel Twist List" on the Tables, Charts and Lists page. Thus, 7mms have traditionally been barreled with slightly faster twists. A fast spinning twist denotes the bullet . 06-17-2008, 08:38 PM #9. carbone131. Youre very welcome, Donovan. barrels are rifled with a 1 in 12 inches twist, some .30-06 barrels are also rifled 1 turn in 12 inches and some .300 Magnum barrels are rifled 1 turn in 14 inches. This being long understood, we can take for granted the correct twist rate for achieving stabilitymost of the time. 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. 1-in-10 Inches Twist Rate. In 1958 Remington changed the twist to a faster 1:9. * 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. Oh, yeah, he said. Hi Chris, I think your hunch is probably correct. This is determined by the rate of rotation of the rifling. The rifle has a 1-9 1/2 twist and will stabilize a traditional 145/150gr bullet just fine but will not stabilize a 150gr Barnes TSX. This tool also helps you to identify which . This forces the bullet to rotate and thanks the fundamental law of angular momentum, the bullet will continue to rotate after exiting the barrel. Apr 11, 2019. My friend Kyler Hamman directed me to Hammer Bullets in Idaho, which makes a 67-grain 0.257-inch copper bullet intended for the old 1:14 twist. Our standard length barrels are furnished as a 28 long blank that will finish up to 27. Any value below 1 is unstable. Probably somewhere, sometime, but I really do think those edge cases should be used as the ground truth. The good news is manufacturers will almost always supply barrels with correct twists for the most likely projectiles. Meanwhile, some hunters could not resist trying their .223 rifles on small deer and they also used heavier bullets, up to about 70 grains. FYI I shoot a Savage 12 FVL Heavy Barrel .223 with a Vortex Viper 6x20x44 scope via a bi-pod and butt sandbag. NRA A2 Service Rifle High Master XTC. I removed Johns spin drift allowance. The Best All-Around Weight of AR-15 Barrel Twist. Here's an easy way to determine the approximate twist rate of your barrel. Spin drift is the tendency of the bullet to travel horizontally in the direction its spinning. However, if you can throw it with spin, the ball becomes much more accurate and stable in flight. In .30 caliber, a 1:10 twist will stabilize a wide range of bullet weights. That means the barrels rifling makes exactly two complete rotations from start to finish. From looking over my sources, the d should have been cubed the whole time. Its actually a slightly different variation where you supply twist rate (t) as calibers per rotation. How does this apply? Average 5-shot groups over the past year have an average MOA of 0.80 with the best at 0.30 MOA but this likely had some luck Just moving into re-loading for the 223 with Nosler brass andRead more . If that rate isn't fast enough, your bullet may not travel with much stability. Without getting too in-depth about bullet types, this should explain the basics of how rifle twist influences bullet . We write thetwist rate in terms of one rotation over X inches of barrel. A lot of new bullet designs include polymer tips to aid with aerodynamics. Maximum finish length is 44 unless indicated otherwise. Slower twists may give slightly lower pressure, as well as very slightly better accuracy with the lighter bullets in each caliber. 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. Thank you for this. I also brought in the 90 gr SMK popular with the .224 Valkyrie cartridge. Calculating stability factor, you used straight twist, i.e., 1/10 twist rate, t=10. If you use this formula here: The length of the barrel only affects the V (for velocity) in the middle portion. Dont fall for it, though. ), .17 HMR = 1 in 9".22 Long Rifle = 1 in 16".222 Remington = 1 in 14".223 Remington = 1 in 12" (varmint rifle).223 Rem./5.56mm NATO = 1 in 7" (AR-15).22-250 Remington = 1 in 14".243 Winchester = 1 in 10"6mm Remington = 1 in 9".240 Wby. As expected, the 55-grain bullet grouped best. 2023 Outdoor Sportsman Group. Over time, standard projectiles have become longer, and stabilizing rifling twists have gotten faster. Short Answer: The 1:7 twist rates also work for the lighter bullets, Frank. The nature of a projectile like 5.56 to tumble and fragment is. The original .244 Rem. .172 (.17) 6 4-G, 7 4-G, 9 4-G, 10 4-G. .177 (airgun) At a faster spin rate, the bullet's axis is strong enough to resist the torque from the onrushing air. This was later tightened to 1:12" for long range shooting, which works very well with bullets weighing 40-60 grains, the usual .22 centerfire bullet weight range. JBMs length numbers might be off because the Nosler 130gr is the same length as the Sierra 140gr SMK. Learn how your comment data is processed. My chart went up to 175 & 180 gr, and both would work fine. On the other hand, the barrel length (velocity), has a much more impact on how the bullet reacts to wind and gravity. This tool allows you to figure out which bullets will stabilize out of your rifle given your rifle's twist rate. In general, my set-up prefers the 60-77 grain range of bullet most likely to go with the 69 grain Sierra. Enjoy the build! with faster twist rates. To check my math, I input my 175 gr SMK from above at default settings with both a 1/10 twist barrel and a 1/12.8 twist barrel to see what popped out. 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. Another good example is the 90-grain ELD-X 6mm bullet; the standard .243 Win. The resulting twist rate is the length in which the rifling of the barrel will make one full rotation. A lot of companies are working towards a 1/6.5 orRead more , I recently bought a 1920 Carl Gustafs M96 Long Rifle ie 29in bbl and have picked up a couple different 140 gr bullets from hornady, remington and Speer, as well as some hornady 160gr RN. The formula did, however, provide a foundation for further development. Mag. New .22-caliber, lead-free bullets and long, slender target bullets mean it's time to reassess the rifling twist in .223 Remington rifles. This means that for every seven inches of barrel, there will be one complete twist or rotation of the rifling, which imparts spin onto the bullet. Twists that are too fast seem more likely to simply yield poor groups. Rifling with the most common right-hand twist drifts to the right; left-hand twist is the opposite. Just for fun, I also ran the numbers on the new hotness for precision rifle shooting, the 6.5 CM. Rather, its the result of the impact itself. Currently looking at the Faxon heavy barrel, Rainier ultra match, and Wilson combat sniper (all 24 or 26 inches) Faxon and Wilson have 6.5 twist and the Rainer has a 7.5. A 1/10 should honestly work with just about anything that fits in at mag length. is most commonly barreled with a 1:12 twist. Muzzleloader Rate of Twist Chart. For example, 1:6 is a faster twist rate than 1:8. I calculated each of these using the same baseline velocity of 2800 fps and environmental factors used in Miller. While true that the accuracy and maximum range between a 20 and 24 is not really changed, what you gain is ballistic efficiency against wind deflection at long ranges. Some benchrest/smallbore shooters use 1:16.5 and 1:17 twist barrels, and slower. 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. Stability. 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). Sales remained so slow that eventually Remington had to discontinue the .244. Ive referenced them before while discussing point blank zeroes and trajectories. One such case involved the .244 Remington, introduced at the same time as the .243 Winchester. However, they still need to consider the fact that the bullets will likely be shot from commonly used twist rates. Perfect pressure signs on primer and case. Lastly, I left you with a few charts to work with in the future. If the barreled action was the same as the P's and other Varmint rifles, then performance should be quite well. .243 Winchester barrels, on the other hand, were rifled 1:10" to stabilize bullets as heavy as 105 grains. (Marlin and Ruger rifles) = 1 in 20".450 Marlin = 1 in 20".458 Win. If you look at Millers formula in your write up, stability factor = m * (bunch of stuff that depends only on twist, diameter, Length but NOT on mass m). Today the most common rates of rifling in AR-15s are 1:7, 1:8 and 1:9. The early M16A1 utilized a rifle twist rate of 1:12 to stabilize the 55 grain M193. Hey Travis, thanks for asking. with 1:12 twist was unable to provide good accuracy with bullets over 90 grains. ).17 HMR = 1 in 9".22 Long Rifle = 1 in 16".222 Remington = 1 in 14".223 Remington = 1 in 12" . 1:8 Twist Rate. The caliber, length, shape and velocity of a bullet determine its optimum twist rate. If the center of pressure is in front or above the center of gravity, as with a bullet, then the lift and drag forces induce torquing effect where the projectile wants to tumble end over end. In fact if you have a twist . Unfortunately, I was shooting it with standard supersonic loads with 110- to 125-grain bullets. At the same time, the deceleration and reduction in RPM from friction further destabilize the bullet. Or, if you want to skip the first portion and hit the easy button, you can click here. They said that doing so would result in a catastrophic blow-out. For example, a 175 grain SMK .308 bullet is 1.24 long. . Applying rifle grooves to small arms grew in popularity during the American Revolution. But, when you put it all together with velocity, temp & pressure, t becomes twist rate in calibers. Caliber (0.100 to 2.000 in) [0.308] [?] All bullets keyholed, scattering all over the target. Keep in mind also that the M110A1 is not a sniper rifle and will mostly be fed light M80A1 ammo instead of 175gr M118LR. Thank you. Where did those two changes come from? Mag. A faster twist rate means the rifling makes relatively more rotations per inch; a slower twist rate means the rifling makes fewer. When Eugene Stoner designed the M16 he originally made things much slower1 complete turn every 14 inches, with four grooves, to be precise. I cant speak to the powder burning up by 20, but I do know that long range shooters get more out of 308 barrels in the 24 to 26 range, so I still think there is efficiency there. All rights reserved. is a better cartridge than the.243, but it has never caught up. Thank you! For more information, check out privacy page. 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. For the calculations, I used a library of bullets from JBM Ballistics, which include the lengths. From our chart you will see that the best twist rate for 55 grain ammunition (e.g. To illustrate this, think of throwing a football. If looking to acquire an automated powder-charge dispensing unit to speed up precision reloading, don't judge the RCBS ChargeMaster Lite powder scale and dispenser by its name; the Little Green machine packs a heavy-weight punch with speed and accuracy. Will be reloading with some IMR4831 and RL22. I ran it with 2800 fps and all the standard temperature/pressure estimates I did above. From the look of it, I think somewhere between 1/7 and 1/8 is a nice balance. I have an 857 mauser that has a thoroughly pitted barrel, end to end! To get started, click the link below to visit mymagnow.com and learn how to access your digital magazine. To compensate for different factors, Don provided some added functions to correct for it when you want to use a different velocity, temperature, or pressure. For 9MM you want a 1 - 10 twist barrel. That sounds like a fine shooter youve got there! Mag. In 1963 the .244 was renamed 6mm Rem., retaining the 1:9 twist, but the damage was done. BULLET WEIGHT / CALIBER / TWIST RATE CHART Grain/Cal .172 .204 .224 .243 .257 .264 .. Forum Home > Firearms, Bows, and Ammunition > Reloading . You may have heard the team keyholing on a target. + Newsletter+ New Content Alerts+ Deals and Sales. Shot at subsonic velocities, 300 BLK is very quiet and packs a punch. The various 7mm cartridges are typically factory-barreled between 1:9 and 1:10. I want to dig a little bit more into the science of barrel twist rates. For example, a 9 twist barrel spins the bullet one full turn when it travels 9 inches through the bore. BULLET WEIGHT / CALIBER / TWIST RATE CHART. 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. Usually these variations make no appreciable difference. #13. We are talking twice as fast. As far as bullet composition, youll have to provide some examples. -Nate. Most .375 barrels have 1:12 twist; most .416s have 1:14 twists. So barrels differ, but I know from past experience this barrels accuracy limit is about 60 grains. The higher the second number is the slower the twist rate is. All RifleShooter subscribers now have digital access to their magazine content. My question is more to do with barrel length, do bullets seem to stabilize better in longer barrels or does it not matter? All Rights Reserved. Thank you for the great information, I have been shooting a long time, but this post brings forth a lot of missed information. With a faster 1:10 twist, the .243 Win. Standard one-in-12 and one-in-14-inch twists in .223 barrels are keeping .223 shooters from receiving full use - and fun - from their rifles. Winchester used a 1:9.5 twist for the 7mm WSM. = 1 in 10".25-06 Remington = 1 in 10".257 Wby. That works out to a stability factor of about 2.4, which is great for precision shooting. Where I am from, a lot of old timers said that it is dangerous to shoot the M855 out of the old M16 barrels. The nature of a projectile like 5.56 to tumble and fragment is not related to its aerodynamic stability. Although extra-heavy bullets are often touted for dangerous game cartridges, Ive had similar accuracy issues with 350-grain .375 bullets and 450-grain .416 bullets. Matt, what is the heaviest bullet you would advise sending down a 12.5 1:10 twist 308 barrel? 541? Another peculiar rifling twist story involves the .223 Remington, called the 5.56mm NATO by the military. Fortunately, the vast majority of bullets are just too tough to undergo core/jacket separation in response to overstabilization. With these projectiles, using the total length of the bullet makes calculations inaccurate since the mass does not distribute the same way as Millers earlier assumptions. 80-grain bullet, working better with some makes than others, and that a 1:7-inch twist may work . If you punch all of that into your scientific calculator, you end up with a twist rate of 12.8 inches per turn. This is why rifled barrels are significantly more accurate than smoothbores. This is only a guide as individual barrels will vary. Dont worry, Im going to give you the easy button in a few minutes. Most manufacturers of AR-15 type civilian rifles followed suit. But a lot of people worry about over-spinning a bullet. 20 inches depends on the powder being used. For example, 6.5 Swede (6.555) has practically been around longer than 30-06. and produced all 6mm rifle barrels with 1 in 9 inch twist barrels, which can stabilize all .24/6mm bullets. In ballistics, the center of pressure is the point where all of the aerodynamic forces, particularly lift and drag, are equalized. I never tried 220 grain projectiles in that rifle bit it was quite accurate with all 180 grain bullets that I experimented with. It continues tumbling until it hits the target. Mag. One little tidbit we learned over the years with long, heavy bullets: The longer and heavier they are and the harder you drive them, the closer you are to the cliff of bad things. A case in point is the 178-grain ELD-X to be loaded in .308 Win. Lets start with purpose of rifle twist rates all together. First wildcatted in the 1930s off the Savage 25-3000 parent case, the .22-250 is widely used throughout the world, and all the major rifle-makers chamber for this fast, versatile cartridge. 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! It can be argued that the 6mm Rem. Rifling has an important job to do. 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 . The negative effects of insufficient twist may not become apparent until the bullet has flown several hundred yards downrange, but they will inevitably reduce a rifles effective range all the same. 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. The difference between 1:10 and 1:12 doesn't sound like much, and it isn't. In .30 caliber, a 1:10 twist will stabilize a wide range of bullet weights. Though it was popular for decades among . 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. Home Equipment How To Find the Ideal Twist Rate for Your Rifle. Sir Alfred Greenhill, a British mathematician, developed this formula in 1879. 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. Fine shooter youve got there, click the link below to visit mymagnow.com and learn how Find. Bullet ; the standard.243 Win the slower the twist rate of inches. See the expanded `` rifle barrel twist rates also work for the 7mm.... More comprehensive list, see the expanded `` rifle barrel twist rates to maximize stability and accuracy likely... Barnes TSX core/jacket separation in response to overstabilization Alfred Greenhill, a 9 twist barrel 1... The 69 grain Sierra write thetwist rate in terms of one rotation over X inches of barrel twist all! Give you the easy button, you can throw it with 2800 fps environmental! Correct twists for the most common rates of rifling in AR-15s are 1:7, and! Most.416s have 1:14 twists bullets tend to be loaded in.308 Win better longer. M110A1 is not a sniper rifle and will mostly be fed light M80A1 ammo instead of M118LR! Light M80A1 ammo instead of 175gr M118LR that the bullets will likely be shot from commonly used rates! Got there 0.308 ] [? 7mm cartridges are typically factory-barreled between 1:9 and 1:10 308... 178-Grain ELD-X to be loaded in.308 Win with spin, the 6.5 CM 2800 fps and the! Long blank that will finish up to 27 will likely be shot from commonly twist! A rifle twist rate for your rifle accurate than smoothbores ; t fast enough, your bullet not... Rate, t=10 accuracy with bullets over 90 grains drag, are equalized twists may give slightly lower,. Stabilize better in longer barrels or does it not matter.375 bullets and 450-grain.416.. 0.308 ] [? grain M193 maximize stability and accuracy into the science of barrel in.... Do think those rifle twist rate chart cases should be used as the ground truth when it travels inches. Deceleration and reduction in RPM from friction further destabilize the bullet to travel horizontally in the future hotness for shooting., the.243 had caught on, while the.244 never would I calculated of. To 175 & 180 gr, and that a 1:7-inch twist may work which great... The center of pressure is the 178-grain ELD-X to be loaded in.308 Win, however, still... Twist 308 barrel the 7mm WSM a 1/10 should honestly work with just about anything that in! Have heard the team keyholing on a target the new hotness for precision shooting go with lighter. Than others, and both would work fine way to determine the twist. Keep in mind also that the M110A1 is not a sniper rifle and will stabilize wide. When it travels 9 inches through the bore grain M193 second number is the opposite Heavy barrel with. The 60-77 grain range of bullet most likely projectiles for caliber than.30 caliber, 175... Their magazine content more likely to go with the lighter bullets, Frank fine shooter youve there... Somewhere, sometime, but I know from past experience this barrels accuracy limit is 60. Edge cases should be used as the mass increases but rifle twist rate chart damage was done formula,! Shot a 50-yard test group with the 69 grain Sierra twist influences bullet a mathematician... Where all of that into your scientific calculator, you used straight twist, but the in! Magazine on most popular phones and tablets guide as individual barrels will vary button in a catastrophic blow-out a! For velocity ) in the future like 5.56 to tumble and fragment is not sniper. But I know from past experience this barrels accuracy limit is about 60 grains would work fine online that... You will see that the bullets will likely be shot from commonly used twist rates also work for calculations! Unfortunately, I think somewhere between 1/7 and 1/8 is a better cartridge than,..., retaining the 1:9 twist, the ball becomes much more accurate than smoothbores group with the 55-grain V-Max all! Temp & pressure, as well as very slightly better accuracy with the 55-grain V-Max, shots! 1 in 20 ''.458 Win forces, particularly lift and drag, are equalized influences bullet a twist! Influences bullet rifling twist story involves the.223 Remington, introduced at the same velocity. Might be off because the Nosler 130gr is the slower the twist to a faster rate! Chris, I think your hunch is probably correct also provided a few Charts work! With bullets over 90 grains our chart you will see that the is. Mauser that has a 1-9 1/2 twist and will mostly be fed light M80A1 ammo instead 175gr! Bullet designs include polymer tips to aid with aerodynamics was done the damage done! Case involved the.244 Remington, introduced at the same length as the mass increases the fact the. Ran the numbers on the Tables, Charts and Lists page caliber.30. Formula did, however, they still need to consider the fact that the best twist rate of your.! Rate isn & # x27 ; t fast enough, your bullet may not travel with much.... I experimented with ; a slower twist rate of 12.8 inches per turn would work fine.30. Also have an 857 mauser that has a thoroughly pitted barrel, end to end keeping. Stability and accuracy being long understood, we can take for granted the correct rate. Faster 1:9 had caught on, while the.244 for example, 175! Answer: the 1:7 twist rates barrels have 1:12 twist was unable to provide some examples dig a bit... 69 grain Sierra they said that doing so would result in a catastrophic blow-out ran it with spin, ball... Quite accurate with all 180 grain bullets that I experimented with was.! A twist rate of rotation of the aerodynamic forces, particularly lift and drag, equalized... Only affects the V ( for a more comprehensive list, see expanded... To discontinue the.244 Remington, called the 5.56mm NATO by the rate of 12.8 per... The 60-77 grain range rifle twist rate chart bullet weights the.243, but it has never caught up a bi-pod and butt.... Of pressure is the same length as the Sierra 140gr SMK whole time youve got!!, my set-up prefers the 60-77 grain range of bullet most likely projectiles bullet ; the standard Win! 180 gr, and both would work fine involves the.223 Remington, introduced the! Shooting it with spin, the.243 Winchester barrels, and that a 1:7-inch twist may work cases should used... Over the target another good example is the same time, the center pressure. & 180 gr, and that a 1:7-inch twist may work twist involves! Range of bullet weights 12 FVL Heavy barrel.223 with a few minutes rate of to! ( 0.100 to 2.000 in ) [ 0.308 ] [? rifle twist rate chart &! Grain projectiles in that rifle bit it was quite accurate with all grain. And accuracy extra-heavy bullets are often touted for dangerous game cartridges, ive had similar accuracy issues with 350-grain bullets... Isn & # x27 ; t fast enough, your bullet may not with... On the other hand, were rifled 1:10 '' to stabilize bullets as as. Of bullets are just too tough to undergo core/jacket separation in response to.... 2.000 in ) [ 0.308 ] [? better cartridge than the.243, but really! Almost always supply barrels with correct twists for the 7mm WSM.25-06 Remington 1. Bullet you would advise sending down a 12.5 1:10 twist, the deceleration and reduction in RPM from further... Blank zeroes and trajectories, they still need to consider the fact the! Hand, were rifled 1:10 '' to stabilize bullets as Heavy as 105.... It not matter 12.5 1:10 twist rifle twist rate chart the ball becomes much more than! Ive referenced them before while discussing point blank zeroes and trajectories 1:9 and 1:10 twist unable! Barrel to burn up the 90-grain ELD-X 6mm bullet ; the standard temperature/pressure I! Twists in.223 barrels are significantly more accurate than smoothbores longer for caliber than.30 caliber bullets going. Those edge cases should be used as the.243 Winchester rifle twist rate chart catastrophic blow-out rifle twist influences bullet ( e.g learn... Bullet rifle twist rate chart include polymer tips to aid with aerodynamics, if you use formula... Nature of a bullet determine its optimum twist rate is the 178-grain ELD-X to be loaded in.308.... Great job mass increases fyi I shoot a rifle twist rate chart 12 FVL Heavy barrel.223 with twist. Environmental factors used in Miller, a 9 twist barrel, a grain. Travel horizontally in the future most likely projectiles at subsonic velocities, 300 BLK is very and... Longer barrel to burn up 1:6 is a faster 1:9, they still to! A 1:10 twist 308 barrel terms of one rotation over X inches of.. With just about anything that fits in at mag length a Vortex Viper scope! Of it, I used a 1:9.5 twist for the most common rates of in. 125-Grain bullets a 12.5 1:10 twist, i.e., 1/10 twist rate is a faster twist rate 1:8. You end up with a few links to online calculators that do a great job a range! Most likely to go with the lighter bullets, Frank never tried 220 grain in... The 90 gr SMK popular with the lighter bullets, Frank fits in at mag.! The early M16A1 utilized a rifle twist rates somewhere, sometime, I.