A longer bullet has to spin faster than a shorter bullet to maintain a stable flight profile. Since all three bullets (55gn, 62gn, and 77gn) are 5.556mm/.223" in diameter, heavier bullets are longer than lighter bullets. So, a 77gn bullet can spin at 1/7" and a 55 gn bullet can spin at 1/9" to maintain a stable flight profile. At longer ranges as bullet spin rate diminishes, it's rotational wobble (bullets angle of attack compared to it's spin axis) increases, reducing stable flight profile and increasing MOA (minute of angle) of flight profile.
I have heard a lot of explanations of twist rate in my day and this I must say has been the MOST simplistic explanation I have heard yet. Too the extent that I had one of my 9 year old shooting students listen to this tonight and she completely understood and expanded on it.... Point being if you don't get it after this explanation, you NEVER will.......
A buddy of mine explained to me just a couple days ago that a bullet is considered "stabilized" when it is rotating through the air at 250,000-300,000 rpm, and this partly explains the different twist rates in barrels.
Definitely 1:9 for the usual shooter. We all use 55gn stuff for training and ammo stock. Honestly though, doing some math with a stability calc + what others have posted online, the 1:8 will stabilize the 77gn just fine and still have some room for error. The 77gn round is the longest that will fit in an AR mag. What I don't understand is why so many companies make the 1:7 twist barrels.. They're everywhere. One thing that happens when you spin a bullet more than it needs to is that accuracy opens up because it's spinning faster and any imperfections in the bullet will open the group up (very slightly). What also happens is you get more spin drift. The bullet stays angled up at the angle it was shot at why flying down range and it starts drifting right as opposed to a properly stabilized bullet. 1:8 or 1:9. I do 1:8 because it will take any bullet that will fit in an AR mag.
This channel needs to be more popular, literally the best most straight forward informative gun channel I’ve come across with none of the clickbait stupid fluff
I really did like the way you explained it. I just shot my very first pistol last week, and I just fired my very first AR-15 today. This video helped me a lot to know my ammo.
Very well said video. The twist rate argument, for most people, is nit picky bullshit. Under 200 yards (what most people's AR's are setup for, and what most people would shoot cheap 55 grain ammo for), Federal XM193 groups as well as 2 MOA in my 1/7 rifle. That's pretty damn respectable. Past 300, things really open up. I believe this has lots to do with 55 grain rounds' bad ballistic coefficient, but I have no doubt that the twist rate exacerbates that, just how you described.
Great video. I've got a 1/8 and a 1/9. Really happy I didn't go with the 1/7 since I only really shoot 55 and 62. Explains a lot! Love your videos even when you talk shit on the ACR ; ) still absolutely love shooting mine from the bench or prone.
Thanks for explaining this to me. I knew it at once upon a time and forgot it. I also knew that if I wanted an explanation without the bullshit, that I had to locate you. You do an awesome job and screw those bastards that are hating.
Football analogy is by far best I've heard. Though the spiral aspect of a throw is basically exactly same concept. And 55gr stabilizes pretty darn good out of all the 1/7s I've had. But just giving you crap. Lol. Great channel subd
I have several AR 15's with 1:9, 1:8 and 1:7. I shoot 55gr---77gr. I shoot whatever I feel like at the time. I just re-zero each scope to whatever ammo I decided to use at that time. I generally shoot 100 yards out to around 600 yards. Something I may shoot 55gr VMAX in 1:7 sometime in the 1:9. Sometimes I may shoot IMI razor core in the 1:7 1:8 or the 1:9. I have never had an issue. All are accurate! If I can take a coyote at 600 yards with any of them I'm happy. I shot a coyote a few days ago at 550 with a 55gr VMAX in an AR with a 1:7 twist. I have a night vision optic on an AR for hogs in my crop fields with a 1:9 and I use IMI 77gr razor core. All are accurate and absolutely deadly. I don't like it over think things and I don't listen to so called experts. I test it and find out what works for me. My advice is don't overthink it and make it complicated. I may be 60yo but I routinely take hogs out to 600 and only miss 1-10 shots or less. I have a 400acre farm and a terrible problem with hogs destroying my crops and hay field. I shoot alot and often. This is my experience with much trial and error and just my opinion.
Good vid and thanks for putting in the time on them. I agree with the conclusions but not exactly in the same way. The twist rate needed to stabilize a bullet is more dependant on the length of the projectile than on the weight. For a typical lead & copper bullet it's not so much a factor. However, a 62 grain M855 bullet is much longer than an all lead 62 grain and therefore needs more twist to stabilize. All copper bullets (GMX, TSX) are long for their weight and need a faster twist. Spinning faster than needed will cause imperfections in the bullet to influence it's path and spread groups. That's why the AMU runs 1-8" barrels on their match rifles instead of 1-7". I hope this helps and doesn't confuse the issue.
Barrel length also comes into play here. The longer the barrel, the slower the twist necessary to stabilize longer heavier bullets. A 16" 1:9 barrel will not stabilize a 77gr bullet as well as a 24" 1:9 barrel. Same twist rate, but the longer barrel stabilizes the bullet better by having more twists before the bullet leaves the barrel. Additionally, spinning a bullet too slow causes the nose to wobble and this is what causes the inaccuracy. Spinning a bullet too fast causes two things, a loss in 'possible' velocity as the bullet is traveling in rifling of more overall length (more resistance to get to the same muzzle) and two, spinning the bullet so fast the centripetal force can cause the bullet to come apart in travel. Over-spinning the bullet rarely causes a degradation in accuracy as long as the bullet survives the forces. Many wildcat rounds over the years have been made with the specific purpose of over-stabilization to assist in using lighter bullets to above average distances. A lot of the initial 220 Swift and 22-250 wildcat guns were like this in the desire of that 1k yard prairie dog shot. The first time you see a 40gr Nosler BT at 4200FPS come apart in the air, you are like, WTF just happened? Bottom line for AR's, all three of these twists will stabilize all three of this bullet weights and everything in between. Any potential loss of accuracy based on twist rate will be nominal in comparison to the bullets drop and wind drift past 300 yards. Out of any 5.56 barrel with these three twists, a 77gr Sierra Match King bullet (the one in the Mk262 ammo) will be more accurate, period. I own 10.5" to 24" barreled AR's with twist rates of all three types. 77gr SMK wins out of all of them with factory and optionally made reloads of any type bullet weight for each gun. Please, test it for yourself.
I know I'm a little late to the party, just doing some research on the subject, but what often makes perfect sense on paper sometimes does not always work the same in reality.
I use my ar 16 inch 1/8 for seals otters and deer. I noticed that 62 g puts everything down pretty good except seal past 200 yds. Mind you that's a moving softball size target and I'm on a boat.
If’s specifically the ratio of the length of the projectile compared to its width that determines the optimum rate of twist for stabilization. Example, if you created a 55 grain .224” caliber bullet with a tungsten core, and compared it side by side to a 55 grain FMJ, (with a lead core), bullet, the tungsten core bullet would be noticeably longer. Your 55 grain, tungsten core bullet would require a greater rate of twist to stabilize it at long ranges, even though its weight is the same. This is why this new M855a1 ammo, even though it has the exact same weight as the M855 bullets, its length is noticeable longer. (The actual projectile, not the loaded cartridge) Because the core of the M855a1 is lead free, to maintain the same weight as the M855, it has to be longer. This will cause it to yaw at longer distances and it’s effectiveness in penetration will not be as efficient.
Green tip 5.56 62 grain vs Remmington .223 55 grain. These are at the same price point. I can't get a definitive answer on what twist rate and/or optimal range. Edit: Let me add to that that the green tip 5.56 steel rod isn't perfectly center for each bullet, or so I've been told. At 100 - 150 yards my group on my 16" 1:8 twist almost exactly 1" tighter than the regular 55 grain fmj.
A high rate of spin and velocity are the ingredients needed to stabilize low drag bullets to get to the greatest distance before the bullet begins to fly erratically and then tumble end over end. From a 1/7 twist 20 inch barrel some 75+ grain .224 bullets can get to the 1000 yard line nose on when powered by an appropriate charge of a suitable powder, like Power Pro 2000 MR. US Service Rifle competition proves that the 1/7 twist also supports the best outcomes in 100 yard reduced course matches where the 52 grain match bullet is boss. The bottom line is get a match grade 1/7 twist cut or button rifled 20 inch barrel with a Wylde or CLE chamber, and then free float it for best accuracy to any distance the bullet can get to nose on from match grade 77 grain ammo. Then, work on Marksmanship development, which can be measured in Service Rifle Competition governed by the CMP or NRA. A good start is signing up for the USAMU’s Small Arms Firing School where you will get instruction without vulgar language.
Twist rate is all relative to bullet length and velocity, the general information presented here is not really accurate, 1:12 will stabilize most loads up to 69gr flat base, 1:9 with a 20" barrel is what is optimal for m855 projectiles, 1:8 will shoot anything that was designed to fit in a magazine.
This is all info that I already knew, but I'm surprised how many "gun guys" don't understand this. As with most of my firearms I take a "middle of the road" approach with my ar15s. I shoot a ton of this cheap federal xm855 lc1 ammo. I pay around. 40 cents per round for it, so I can shoot a lot for my money. I like barrels in the 1/8 twist variety be cause it works well for the ammo I have 1000s of rds of and it will also work ok with anything else I'm likely to get my hands on in a SHTF situation. Great video, I really enjoy the content you put out there.
Not true. 55 grain stabilized just fine in a 1 and 7. thats what we used for qual in the Marine Corps out to 500 yards. worked just fine, accuracy was spot on. all of those grains will work just fine in a 1/7 barrel.
You act like I say that it wouldn't do the job at all... which is exactly not what I said. Pay attention, there's a difference between it being doable and optimum performance.... which is what im talking about. Also your targets at 500 are fucking gigantic, and you use an aperture sighting system that doesn't make you hold over for anything. so that's not exactly a fantastic way to judge the difference.
Good info.Especially for those who are new to the ar platform.Having been around ak47s and military surplus rifles most of my life just purchased my first ar15.It is a different animal.Do your! research before you buy.Informed decisions are always. best! Once again thanks!
some people say it really doesnt matter under 300 yards - ill be honest...im even seeing the difference at 100-200 yards. My Mk12 build with my 1/7 barrel has a muchhhhhhh larger grouping at 100 yards with m193 than it does with 77 grain 5.56. I mean the group is half the size. It really does make a difference. When I say "half" im talking a 2 inch group down to a sub MOA group. but like you said - the further you take that...that 2 inch group turns into a 6-8 inch group
Not sure how this answered any questions. Bbl really doesn't matter, optimal twist rates vary by caliber... lighter/shorter bullets need less spin. Lightly constructed bullets may come apart if spun too fast, NOT common. No mil-spec ball round will be super accurate at long range, too little spin just makes it worse.
Thx, so sounds like the 1:8 barrel is preferred over the 1:7? I’m asking to confirm from your comments - you used “pretty good” as the best performance term for the 1:8 and “OK” as the best term for the 1:7. Doesn’t appear that the 1:7 gets there or do we need to be using heavier than 77 for 1:7?
77 grain bullets are quite expensive to be shooting paper. 1/9 is the twist rate i prefer since the 55 grain is cheaper and very common. Thanks for the vid :)
Best explanaton. Ive seen in a while ,.keep it simple. Ill take 1/9 for everyday training,.. it'll go up to 69 gr easily,.. maybe if its a good bbl,(DD)...75 gr. The problem the military had with 62 gr ammo stabilizing was with 1/12 twist bbls I think or thought
i have a cuestion... here "switzerland" i use the 62 grains gp90 in 1-10 "standart" Twist rate... we know that our sig 550/551/552 can use any Kind of ammo, but not the AR rifle... so what Twist rate are the best for our ammo? thanks and very good explain...
The faster the twist rate, (smaller 2nd number).the "faster" the twist and/or spin of projectile. Faster rate (like 1/7) typically stabilizes heavier grain weights, though projectile length also plays a role. But I agree with your take. 1/9 best for 55gr, 1/7 better for 77gr, though 62gr as well. While 1/8 does great for both mil rounds, 55gr and 62gr
I know everyone has a different spin on this subject. I have a very close friend who works for H&K. They specifically state anything under 65 gr is best with 1:7 twist using 5.56. I saw another video where a guy was saying heavier with 1:7 and when testing, he held a better group over 70 grain with 1:9 twist.
Twist rate is relative to bullet length not weight, even though weight and length usually go hand in hand. Just thought i would make things really complicated for no reason.
One in eight was my choice after a lot of time watching video's online, seeing ones like this. What ever you have will do OK but m855 and 62gr is the best of the three. I still like 25yard zero to make great shots out to 300 yards and just a little adjustment for other distances along the way, except for 25yards. That's a give me.
Thanks. Ill be looking for 1:8 so I can still be able to shoot 55g mainly for practice and 62g for main just in case and 77g if that’s all I can find in some fantasy scavenging😂
so 12.5 inch barrel with 1:8 twist, i should still go with the 62 grain ideally? i it was thinking to get some heavier stuff for the shorter barrel, instead should I be comfortable stocking up on 55gr?
I'll stick with my 123gr 76.2x39 lol jkjk. The .223 is a good round for tumbling when it comes from a rifle length barrel. I learned a lot so thanks for the video.
