| February 7th, 2015 The Applied Ballistics team tested six (6) same-length/same-contour Bartlein barrels to observe how twist rate might affect muzzle velocity. This unique, multi-barrel test is featured in the book Modern Advancements in Long Range Shooting. That book includes many other fascinating field tests, including a comprehensive chronograph comparison. Barrel Twist Rate vs. Velocity — What Tests Reveal
by Bryan Litz
When considering barrel twist rates, itâs a common belief that faster twist rates will reduce muzzle velocity. The thinking is that the faster twist rate will resist forward motion of the bullet and slow it down. There are anecdotal accounts of this, such as when someone replaces a barrel of one brand/twist with a different brand and twist and observes a different muzzle velocity. But how do you know the twist rate is what affected muzzle velocity and not the barrel finish, or bore/groove dimensions? Did you use the same chronograph to measure velocity from both barrels? Do you really trust your chronograph? Savage Test Rifle with Six Bartlein Barrels
 Most shooters donât have access to the equipment required to fully explore questions like this. These are exactly the kinds of things we examine in the book Modern Advancements in Long Range Shooting. In that book, we present experiments conducted in the Applied Ballistics lab. Some of those experiments took on a “Myth Buster” tone as we sought to confirm (or deny) popular pre-conceptions. For example, hereâs how we approached the question of barrel twist and muzzle velocity. Six .308 Win Barrels from Bartlein — All Shot from the Same Rifle
We acquired six (6) barrels from the same manufacturer (Bartlein), all the same length and contour, and all chambered with the same reamer (SAAMI spec .308 Winchester). All these barrels were fitted to the same Savage Precision Target action, and fired from the same stock, and bench set-up. Common ammo was fired from all six barrels having different twist rates and rifling configurations. In this way, weâre truly able to compare what effect the actual twist rate has on muzzle velocity with a reasonable degree of confidence. Prior to live fire testing, we explored the theoretical basis of the project, doing the physics. In this case, an energy balance is presented which predicts how much velocity you should expect to lose for a bullet thatâs got a little more rotational energy from the faster twist. In the case of the .30 caliber 175 grain bullets, the math predicts a loss of 1.25 fps per inch-unit of barrel twist (e.g. a 1:8″ twist is predicted to be 1.25 fps slower than a 1:9″ twist). Above, data shows relationship between Twist Rate and Muzzle Velocity (MV) for various barrel twist rates and rifling types. From fast to slow, the three 1:10″ twist barrels are: 5R (canted land), 5 Groove, 5 Groove left-hand twist. We proceeded with the testing in all 6 barrels from 1:8â to 1:12â. After all the smoke cleared, we found that muzzle velocity correlates to twist rate at the rate of approximately 1.33 fps per inch of twist. In other words, your velocity is reduced by about 5 fps if you go from a 1:12â twist to a 1:8â twist. [Editor: That’s a surprising number — much less than most folks would predict.] In this case the math prediction was pretty close, and we have to remember that thereâs always uncertainty in the live fire results. Uncertainty is always considered in terms of what conclusions the results can actually support with confidence. This is just a brief synopsis of a single test case. The coverage of twist rates in Modern Advancements in Long-Range Shooting is more detailed, with multiple live fire tests. Results are extrapolated for other calibers and bullet weights. Needless to say, the question of “how twist rate affects muzzle velocity” is fully answered. Other chapters in the book’s twist rate section include:
·Stability and Drag â Supersonic
·Stability and Drag â Transonic
·Spin Rate Decay
·Effect of Twist rate on Precision Other sections of the book include: Modern Rifles, Scopes, and Bullets as well as Advancements in Predictive Modeling. This book is sold through the Applied Ballistics online store. Modern Advancements in Long Range Shooting is also available in eBook format in the Amazon Kindle store.
Similar Posts:Share the post "Does Barrel Twist Rate Affect Muzzle Velocity? (Litz Test)" 30 Responses to “Does Barrel Twist Rate Affect Muzzle Velocity? (Litz Test)”Guy says: Excellent piece, very interesting. A interesting test would be accuracy, optimal twist for a certain bullet then shot through faster and faster twists. After shooting service and match rifle ,223 for many years ive used 6.5, 7, 7.7 and 8 twist barrels and found they will even shoot the light stuff very well like 52`s. Richard says: More of this stuff for the Bulletin, please. Stu says: Would love to see a follow-on with accuracy for different weight cast bullets. Including some rather heavy ones… Gaz Morris says: Given the SDs and MV differences involved here, the relationship shown is as likely to be pure chance as not. This numbers shown do not convincingly demonstrate any relationship between twist rate and muzzle velocity. Gaz Morris Doug says: You can do a regression analysis but i bet the r2is low.. The 8.25. 10 and 12 results are not significantly different.. I would guess the author hasn’t had statistics.. I won’t be buying this book. Thanks for the interest guys, glad to know the info is well received. Guy,
I did this test as well, although with .30 cal, and the results are in the book. Stu,
Unfortunately, I don’t have any testing with cast bullets planned other than .22RF. This year will see expansion down to .17, .20, .22RF and up to .416 and .510 caliber. Can only take on so much at once! Take care,
-Bryan Just so no-one comes away with the wrong idea… This test shows that MV can be affected by twist rate, and how much. HOWEVER, the big picture result is that the relationship is so weak that it’s almost lost in the noise. What’s 1.25 fps compared to your shot-to-shot MV variation? Forrest for the trees -Bryan Ian says: So nice to see a quantitative approach to what have been subjective opinions. It would be nice to see other “isms” tackled in a similar way such as barrel break-in Christopher Lollini says: Bryan, While I’m surprised at the small difference in velocity, I’m curious if that correlates to a similar (small) difference in pressure, or is the relationship between velocity, twist and pressure not linear? Chris (MQ1) Chappy says: Mr. Litz, Who’s bipod is that it did you build it yourself? Gaz, You’re somewhat right. The scatter in the data and the R squared value indicate that only about 1/2 the variation in MV is due to twist rate (Correlation Coefficient is 0.55) which means that random noise has as much effect as twist rate. This is discussed further in the book, as well as similar results presented for a different bullet in which the relationship was even weaker, and the correlation was lower. The point in presenting these results is to show that the effect of twist rate on MV is VERY minor, and can almost be said to be statistically “in the noise”. Again, it’s explained in more detail in the book. Results were distilled here for blog content. Take care,
-Bryan Blake Coates says: It would be interesting to see what the pressure curve look like for the different twist rates. In theory the 1:8″ twist would have a higher peak pressure. Bryan – Been a fan ever since your first article in Precision Shooting 7-8 years ago – fantastic work answering the question of how much more of the total energy from the powder charge is lost through the conversion into gyroscopic energy with the faster twist rates! I have always wondered (and Blake Coates kind of touches on this too) about how different twist rates affect peak chamber pressures, and that instead maybe the faster twist rates might produce higher pressures, necessitating a voluntary reduction in powder charge which might have of a significant effect on attainable muzzle velocities. This is a long-held notion that gets thrown around a lot in the discussions (mostly arguments) with buddies much like topic of b.c. and wind deflection was before your first book came out and basically put that one to rest. To test for this effect might not be feasible, but was wondering what your opinions are regarding this. About 1/2 way through the latest book – great stuff. Keep it up! Agree with nightowl, unless pressure testing was done with this test the results are meaningless. We load for a barrel based on accuracy velocity and what we can see for pressure signs. Can we get more velocity with the same pressures? that is the root of this discussion since the Question was asked. bob says: I’d like to see something with a greater range of tests, I wouldn’t think a 308 would vary much between an 1-8 and 1-12. Perhaps a 6br with a 55g through a 1-15 through a 1-8 would show more interesting results. Chris says: I wouldn’t really expect much difference with the same load, I am very curious to see what would happen if you found max loads based upon pressure and then tested velocity from each barrel. It is still good information and nice to see people tackling these kind of questions. For the most part the twist rate doesn’t have an effect on pressures. We make a ton of ammunition pressure test and accuracy test barrels as well. All the feedback I’ve gotten on pressure test barrels is that the twist again doesn’t really effect pressure. Changing the bore/groove size (total surface area of the bore) and or changing the chamber reamer/throat specs. is going to have a bigger impact on pressures and velocities. I have to praise Bryan for taking the time to do the test and taking as many variables out of the equation as possible to get good and consistent data. You won’t get a commercial gun or ammo maker to make this information public etc… Later,Frank
Bartlein Barrels Bob,
The book presents calculated twist/MV effects for other examples from .22 to .338 caliber. Since the calculations were validated for .308 thru live fire testing, it’s reasonable to have confidence in the calculations for other scenarios.
The long and short of it is that regardless of caliber and bullet weight, twist rate has very little effect on MV. You’ll see more fps difference per inch of twist on a .220 Swift just because you’re dealing with higher velocities. In other words, the percentage of MV change due to twist is pretty consistent. Jim,
The test directly addresses the question about twist rate and MV which was the intent. Many people have held the belief that twist rate had a dramatic effect on MV. This was proven false. That result has meaning. Twist rate and pressure is a slightly different question, but it has the same answer. Due to the physics involved, there’s really no mechanism for twist rate alone to affect pressure or MV very much at all. Propelling the bullet forward takes up 99.4% of the energy. 0.6% of the energy is in rotation. If you increase the twist rate from 1:10″ to 1:8″, you’ve increased the energy in the 0.6% portion of rotation, which subtracts from the 99.4% of forward motion. Point being, the forward motion (99.4%) is not affected much by changing the 0.6% component. If you’re working up a load for a 1:8″ twist and it shows pressure at a lower MV compared to a 1:10″ twist, then it’s due to something other than twist such as bore/groove diameter, bore finish, fouling state, etc. In other words, the twist rate is not the causal element in making more pressure. The point of deliberate scientific testing is to isolate variables of interest to determine true causality. It’s important to understand causality because that’s what informs your decisions. It would be a shame if, for example, you chose a slower twist rate than was ideal for your bullet because you had the false belief that you would be giving up velocity (at the same pressure) from the faster twist. You would ultimately be leaving performance on the table because of a false understanding of causality. Frank,
Thanks for sharing your observations on this topic as well. This is an important topic to have a consensus on; considering the importance of twist rate on ballistic performance at long range. -Bryan Kris says: Great article. The effects are pretty negligible. A lot of the things that people harp either have small effects on muzzle velocity or are negated by reloading. You see differences with ammo that is loaded the same that you wouldn’t necessarily see if you were tuning the ammo to each individual barrel. I’m going to agree with you Bryan that it is a small component of the equation, very small. But what many reloaders wont do to get a 2% increase in velocity for a competitive edge. You might consult with Brian Mirnak on twist vs velocity in the testing he has been doing with 155 grain palma bullets. At the time I was in contact with him I was shooting them out of a 17 twist at velocities I won’t quote here, they would one hole at 100 yards but open to 1.5 moa at 600 for obvious reasons, but the point was to push the envelope to the edge of what we were testing with a limited budget. I feel like a true evaluation is best conducted on the extremes, if in fact we want to draw a conclusion from twist rate alone. Lets run the same test with a 18″ 17 twist and a 18″ 7.5 twist, pressure sensors attached, load work-up to pressures within +- .5% using 3 different powders and bullets. With the large separation of twist values we should negate a .0002″ bore or groove discrepancy, obviously cut rifled barrels using the same lot of steel and rifling hooks. If we see less than a 150 fps velocity change we can put this to bed as a myth, as it would amount to as little as less than 15 fps per 1″ of twist. Frank and Bryan, It’s always important to hear what everybody’s wondering about & then hear from some guys in-the-know regarding whatever the topic of discussion might be, so thanks for taking the time to respond. I think you’d be stunned at what some guys have done in terms of decisions (myself included) when building rifles based on some of the long-held beliefs that get perpetuated somehow. Usually it’s by folks that have not taken the time or effort to flush out these ideas to see if they are actually true or just old wive’s tales. Sometimes it’s a case of a faulty understanding of the real science that’s actually at play that leads to an incorrect interpretation of what someone “saw” a few times during a flawed ‘experiment’, a day at the range, or during a hunt. Bryan, sure wish I’d had your first book fifteen years ago – it has been pivotal in helping to finally explain some events witnessed during a few long-range groundhog hunts that had otherwise defied conventional wisdom and left us mystified for many, many years. It has finally made sense of a lot of supposed ‘explanations’ of things that just never seemed to add up. It also effectively silenced some very heated arguments about b.c. and it’s effects. Not to mention that it would have saved me a bunch of money by getting barrel selection right the first time! Written and explained in a way that I can actually understand it (albeit after reading it a few times so it could sink-in to my thick head), the book has quickly become a prized and frequently referenced tool.
(guess this officially makes me a “fan-boy” now – oh well, so be it). Gents, you really need to read these books. I can’t emphasize that enough. So, I’ll stop gushing about Bryan’s books and say I think we can pretty much chalk up another historical ‘hot topic’ of debate that’s been fairly well laid to rest finally by some smart guys with ACTUAL first-hand knowledge and experience on the subject. Though, I have to admit, I’d still really love to see some actual piezo pressure trace data for my own curiosity.
Thanks again. Guy says: I think the bottom line here is twist does not effect velocity to any significant measure. Not a big surprise to the .223 shooter that has used bullets from 40-90 grains and barrels as fast 6.5 twist. Interesting test results showing minimal reduction in velocity from increasing twist rates. I have a 1 in 8 Tikka t3 in .223. but did not have equipment to test it. One point, there must come a point with ever faster twist when the angle of pitch is too high. Wonder what is it for .223. I note none seem to go below 6.5. Brent says: I applaud the efforts of you and your team in collecting, analyzing, and sharing the data youâve presented. Your efforts are aiding in one day finding an answer to the question youâve posed.
Unfortunately, I find your analysis and comments misleading. Whether due to ignorance or misrepresentation I cannot ascertain. Specifically,
âThis test shows that MV can be effected by twist rate, and how much.â
–Your data show a trend in twist rate only; in other words the graph is the best piece of information. There is no statistical significance with which to draw any conclusion. While necessary to analyze the data, reproducing the MV/SD table only confuses the issue to those not familiar with statistical analysis. In other words, your test shows the need for further tests in order to draw any sort of conclusion.
–How much is entirely unanswerable. R^2 should be 2 or 3 standard deviations if you want to answer that question. You simply donât have statistically significant results with which to draw a conclusion. âYouâre somewhat right. The scatter in the data and the R squared value indicate that only about 1/2 the variation in MV is due to twist rate (Correlation Coefficient is 0.55) which means that random noise has as much effect as twist rate.â
–The scatter in the data and the R^2 value indicate a Design of Experiments or similar test need to be conducted to find the significant contributors to the poor fit of the data to the regression line. Once identified, these factors, hopefully can be controlled for. Costs will increase with increased precision in your measurements whether due to more expensive equipment, a larger number of iterations, etc.
–The scatter in the data at this point only indicates that there is too much variability to draw any conclusion. Youâre suggesting that the hypothesis you are testing concerning velocity vs. twist rate is showing a correlation in your results. I and others, above, are telling you that the fit of the data here is insufficient to draw that conclusion although it remains a probability. âThe point in presenting these results is to show that the effect of twist rate on MV is VERY minor, and can almost be said to be statistically âin the noiseâ.â
–There is too much variability in the data with which to draw any conclusion except the need for further data collection.
–The point of presenting the data is to further everyoneâs understanding, correct? I commend you. Thank you. Your interpretation of the results in incorrect. âThe point of deliberate scientific testing is to isolate variables of interest to determine true causality.â
–Agreed. Youâve a responsibility to identify, isolate, and control for those variables prior to drawing any conclusions. R^2 of .5XX isnât demonstrating a significant data fit with which to draw any conslusions.
–Ideally, the true scientific method would include not only your future statistically significant data set, but also those from two other independent sources corroborating your results. I take issue with how youâve presented your findings and mislead others. Why would I purchase this book after youâve either misrepresented or misinterpreted your results? secretaryns says: Mr. Litz, Would you mind telling us how many rounds were fired for each group? The SD of MV values you obtained are very interesting to me. 7 fps is very low and indicative of great control, especially given that A) they’re .30 cal rifle rounds, and B) you managed to do it twice. Since I’m not a statistical analyst ; bean-counter , or Physicist , I found the information interesting . It does tend to follow the idioms of general science in disclosing that ; though twist rates do have some effect on MV , that effect is so minimal , that it is generally irrelevant to the discussion . Unless you want to verbally joust with semantics , or split procedural mathematical hairs . My understanding is that this was a basic test to establish any relationship between barrel twist rates , and loss , or gain in MV thru the different TR’s . To this end ; the data supplied showed “minimal” variations. In doing “Ladder” tests we don’t need to fire 10,000 rounds to get a correlation between a workable charge weight and the “junk” , so why call for excessive rounds testing to prove , or dis-prove a theory , when a sufficient amount of “Base” data is pointing in any given direction ? Is this test absolute ? No….But it does substantiate generally accepted ideology , if one has a basic working knowledge of ballistics . And is it really “that” important ? Personally ; I think not . And since we’re all expressing opinions here , I guess those who are suggesting shooting max pressure charges over a long testing regime have never seen the results of a HP rifle blow up. I don’t hear any of you folks volunteering to pull the trigger for that . Seriously ? Capt. Steve Thompson says: LOL. What is means is the delta ain’t worth spit. Thank You. I know this thread is old but I wonder how the results might be impacted if the bullets were a much heavier (250-300gr) .452 caliber such as the 450 Bushmaster? There’s a lot more surface area on them due to their circumference and they use magnum pistol powders. A debate is constantly going on over on the forum, about going from 1:24 twist barrels, down to 1:16, including one brand of barrel that is 1:10! Enough field observations that have come in show an increase in velocity with the faster twists, so it is assumed that is the result or more pressure. Thanks, Hoot Gentlemen, 1 foot equals 12 inches; 1 minute equals 60 seconds; 1 pound equals 32.17405 slugs “mass”, 1 revolution per second equals 1 hertz, if we don’t quiver on the distance from the center of the Earth (gravity), ambient temperature, barometric pressure, relative humidity, etc. then it boils down to simple arithmetic with wild-ass variables involved. So, lets take a hypothetical gun, barrel length, twist, caliber, bullet weight, etc.. Lets not make it too complicated and loose the battalion of Marines before we reach the beach and end up having to resort to a dog paddle and bayonet gripped by the teeth, or gums. A 24 inch barrel with a 1:18 twist will achieve 2,820 fps, hypothetically, because according to the blog there is a 0.6% loss to the twist, which translates to the loss of 1 fps per inch of twist. If there were no twist, the bullet would exit at 3,000 fps, if the twist rate was infinite, the bullet would never leave the muzzle because it is still twisting as I am typing, and the pressure would be at its maximum and decreasing by the value of e^(-t/T). As you can see in this thought experiment that the twist rate does affect muzzle velocity, but very insignificantly to the point that it is a better trade-off to go with the maximum twist rate for bullet stability at the intended target range than to retain maximum velocity. The worst hit in history is still better than the best miss in history.
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