ideal rate of twist (MLP firearms and shooting thread)

Discussion in 'The Backstage' started by Frogfur, Jul 4, 2017.

  1. Roberteaux

    Roberteaux GOOMPH! V.I.P. Member

    Messages:
    24,561
    Likes Received:
    119,296
    Joined:
    Oct 28, 2010
    Let's start here:

    The original M16 rifle was designed to fire a cartridge that was more or less identical to the .223 Remington, except that it featured a larger powder charge. The bullet weight was 55 grains. It was a solid lead core coated with copper everywhere except at the ass end of the bullet and it looks like this:

    [​IMG]

    The cartridge that featured this type of projectile is known as M193 ball.

    The M16 fired M193. The rifle featured barrels with a 1:12 twist. During its development, it was found that a 55-grain bullet with a cannelure (the ribbed area of the bullet, where it's crimped) featured terminal ballistics that were advantageously erratic. This bullet did crazy things when it hit animal meat-- it would yaw, tumble, and veer, which created a dramatically larger wound cavity. In some cases, the bullet was observed to break in two at the cannelure, and to create two perfectly ghastly wound channels.

    The reason the bullet did all that crazy shit was because a 1:12 twist was sufficient to keep the bullet stable enough in flight that it was suitably accurate for military purposes-- but once it hit animal tissue it became extremely unstable. As was construed at the time, "sufficient accuracy" boiled down to a 2" group at 100 yards.

    The M16A1 came along in the late 60's. It, too, had a 1:12 twist. So, from the early 60's though the early 80's, that's what we were using: rifles with barrels that had a 1:12 twist, with 55 grain M193. The rifle was accurate enough to hit a man with out to about 460 meters (or 503 yards), which was the max distance all US Marines and some Army units engaged targets at during training. From the early Sixties to the early 80's, the US armed forces stayed with this combination of M16 and M16A1 rifles and M193 ball.

    During those years, other NATO member nations tended to issue main battle rifles that were chambered for a much larger and more powerful cartridge, 7.62 x 51mm NATO. But in the early 80's, they saw an advantage in going with a cartridge based on m193 ball. Chiefest of all advantages was this: the average soldier could carry one hell of a lot more ammo than an enemy soldier using a larger cartridge. Another advantage was that the much lower recoil caused the accuracy of the average marksman to go up considerably.

    Their brainchild came to be the SS109 projectile, loaded into a cartridge which (in the US) is called M855, aka 5.56 x 45mm NATO. This is a 62-grain bullet with a three part construction. Basically, it's a steel penetration tip sitting atop a lead slug, and fully coated with a copper jacket. Here's a cross section of the SS109 bullet:

    [​IMG]


    This changed the nature of the round quite a bit. To stabilize this longer bullet, the twist rate of the barrel was tightened. There was a succession of developments: 1:9, 1:8, and finally the 1:7 twist that it standard for NATO barrels these days. Forever freaky, Ruger produced various models that featured a 1:10 twist.

    The trick is only this:

    Within a caliber class, the longer a bullet is, the tighter a rifling twist is needed if the bullet is to adhere to accuracy standards. The NATO document that prescribed the specs for 5.56 NATO ammo is known as STANAG 4172. This is a formal written guideline. You might say it's an international MILSPEC. You can find the doc here:

    http://standards.globalspec.com/std/261371/nato-stanag-4172

    The accuracy spec set forth by STANAG 4172 boils down to a 2" group at 100 yards-- same as M193 specs called for. Any greater accuracy was considered to be superfluous when it came to mass military purposes-- though in most cases greater accuracy than this was achieved anyway.

    When you fire a lighter, shorter bullet through a tighter rifling twist, the bullet doesn't become any more or less accurate. That is, the original, mass-produced M16 rifle with a 1:12 twist is just as accurate as the M16A2 and others are with their 1:7 barrels-- if you're firing 55 grain bullets through both.

    Without a tighter twist, a longer projectile is liable to do weird stuff like keyhole, veer off laterally, and so on because a really loose twist isn't enough to stabilize it in flight.

    Here's a photo of three types of bullets that I currently load for the three rifles I have that feature NATO chambers:

    [​IMG]

    From left to right: 62-grain steel core, 55-grain soft point, 55-grain full metal jacket.

    As you can see, the 62 grain bullet is much longer than the two 55 grain samples. The change in sectional density of the longer bullet calls for a tighter twist, or it won't come up to the accuracy standards set forth by STANAG 4172.

    ***************​

    You can get into .224" bullets that are much longer-- and considerably shorter-- though the really radical short end of the spectrum is more suitable for firing out of a bolt-action rifle or single-shot pistol than anything else. As always, design affects function.

    Here's a photo of a 90-grain bullet standing alongside a 35-grain bullet:

    [​IMG]

    The really short bullets are not often loaded into semiautomatic rifles. It can be done, but it's not a best practice or particularly advantageous to do so. Those are used mainly by varmint shooters, usually firing a bolt rifle with a .223 Rem chamber.

    The long ones are often used by service match competitors using AR rifles. The trick is to be very mindful of bullet seating depth.

    ***************​

    Now, somebody asked about varmint rifles. Most .223 varmint rifles of the bolt-action type feature a 1:12 twist... but then, varminters tend to go with very light bullets that more or less explode when they hit the critter they wish to eliminate. They also propel those projectiles to velocities that are unusually high, within the caliber class. And varmint rifles are often highly accurized. So here again we see that a 1:12 twist doesn't affect accuracy-- so long as one's bullets are sufficiently short and light.

    ***************​

    It is also worth noting that during the conventions it took to establish STANAG 4172 and to agree on a NATO round in 5.56mm, that the idea of "humanity" was taken into consideration. That is, the other member nations were kind of queasy about the M193 ammunition and its spectacularly destructive effects.

    It was found that the longer 62-grain bullet, traveling at a lower velocity, had a tendency to just kind of drill straight through animal tissue, without doing all the erratic dirty work the higher-speed M193 was good for. So that's all nice and humane. :thumb:

    But there are advantages and disadvantages to both projectiles. Though generally more destructive on animal tissue, the earlier M193 was prone to deflect off very light cover-- such as tree branches and so forth-- without even hitting the enemy. The 855 tends to plow through that kind of stuff better.

    But, reports coming back from combat zones seem to strongly indicate that the M855 has the distinct disadvantage of not producing wounds sufficient to stop an enemy from continuing to fight after a direct hit or two. So now the military is back to the drawing board and trying to figure out a solution. It really sucks to hit an enemy, but he's still able to fire back-- and then he kills your ass.

    Their solution so far seems to be a round called M855a1... but this may not be satisfactory.

    Some think tanks are contemplating moving up to a larger round, such as 243 Winchester and the like. The drawback, of course, will be that the average soldier won't be able to carry as many rounds as with the M855 or M193.

    There are other chamberings that work with AR-15/M-16/M-4 type rifles. The two most famous are 6.8 SPC and 6.5 Grendel, but it is not known to me if the military is attracted to these cartridges or not.

    --R
     
    Last edited: Jul 5, 2017
  2. Roberteaux

    Roberteaux GOOMPH! V.I.P. Member

    Messages:
    24,561
    Likes Received:
    119,296
    Joined:
    Oct 28, 2010
    Basically, the deal is like this: if you stick with a semiautomatic rifle based on 5.56 NATO, like an AR-15-- but want to go with heavier bullets-- you have to be very careful to ensure that your rounds end up no longer than 2.260".

    The reason? It's because if they're longer than 2.260, your cartridges won't fit in your magazine! :shock:

    It's also the case that an even longer cartridge might end up etching against the rough lands of the throat (or leade). You don't want that because chamber pressure skyrockets and you might damage your rifle... and maybe yourself. So the Holy Number for M193, 5.56 NATO, and .223 Remington is given as 2.260" maximum over all length. And that is per the standards of both SAAMI and STANAG 4172.

    You can use bullets from 35-90 grains and feed 'em into an AR-15... guys shooting service matches with AR's go in for bullets between 68 and 90 grains, because the heavier bullets have a greater ability to buck wind and feature better flight stability-- given a sufficient twist rate in the barrel.

    The trade-off is that the heavier bullet travels at nowhere nearly the velocity of a 55 or 62 grain projectile. Velocities of around 2,300 to 2,600 are more or less the norm with the heaviest bullets. That's a far cry from the blistering 3,200 fps of M193-- or even the slightly pokier M855, which exits the snout of a 20" AR barrel at about 3,000 fps.

    The minimum cartridge length in 5.56 NATO chambers is often cited as being 2.200"... six hundredths below maximum. But once you get into the super-light 30 grain varmint bullets, the cartridge length decreases to about 2.100"... or slightly less. I've seen specs that read down to 2.088" with 30-grainers.

    These are high-velocity little bastards, and are capable of great accuracy-- but not out of an AR. The longer leade of the AR, combined with the greater jump the small bullet makes in the chamber before getting to the throat, tend to erode accuracy dramatically.

    The little bullets are really best suited for a .223 chamber with its shorter leade, and a bolt-action rifle. Guys who are really serious about the kind of accuracy they're capable of often have custom made barrels with chambers to optimize short cartridges.

    The little guys also tend to run out of steam a bit more quickly than their heavier counterparts.

    There's always a trade-off.

    --R
     
    Last edited: Jul 5, 2017
  3. PeteK

    PeteK Senior Member

    Messages:
    10,010
    Likes Received:
    19,828
    Joined:
    Jul 16, 2009
    Gun nuts when they get a chance to talk about guns:

    [​IMG]
     
    Barker, wizard1183 and FennRx like this.
  4. Roberteaux

    Roberteaux GOOMPH! V.I.P. Member

    Messages:
    24,561
    Likes Received:
    119,296
    Joined:
    Oct 28, 2010

    Yes, I've often noted your disdain for those who are interested in firearms.

    Basically, you seem to always wish to characterize those who enjoy the subject area as being inordinately obsessive, with all the negative connotations thereof attached.

    But do you attach the same negative connotations to those who are quite as interested in any other complicated subject?

    I'll bet you don't.

    When it comes to firearms, you talk about people performing shoulder rolls while engaging make believe terrorists, but ignore the thousands of citizens who have legally defended themselves with firearms against real criminals-- and all without a shoulder roll... and in the majority of cases without even firing a shot.

    You wish to characterize those who have an interest in firearms as being somehow akin to, say, Tackleberry. I guess it helps you psychologically somehow, to wish to invalidate the sanity of others while imputing that they're a bunch of drooling loons who can't wait to shoot somebody. Not sure why you find it necessary to insult others, though I have my suspicions.

    And you seem to wish to assign this kind of thing to all of us-- even though you usually also issue some ritual disclaimer about how you own a couple of firearms, without being so evil as to actually know something about those firearms. Instead, you profess ignorance of the overall subject in general-- as if this is somehow virtuous.

    It's not an indication of mental stability or an obsession that has some erotic quality, to be interested in firearms. That's all in your imagination-- the thoughts of a civilian who has done nothing but to own a couple of firearms you know little about.

    There's a reason we never let you in on the cat avatar thing that you railed about for days afterwards. It's because you're a sarcastic, condescending type, who figures you've got everything wired and can therefore get mouthy in a disdainful manner. But if you can't be mannerly, why show up at all?

    No need to insult others. There's nothing so great about you that you even deserve to act like that.

    And don't tell me this was some joke. You've run your mouth about your feelings one too many times to make that claim in a convincing manner.

    --R
     
    Last edited: Jul 4, 2017
    KP, Hairless_Ape, smk506 and 3 others like this.
  5. PeteK

    PeteK Senior Member

    Messages:
    10,010
    Likes Received:
    19,828
    Joined:
    Jul 16, 2009
    You sure make a lot of assumptions. Yes, I'm sarcastic, I'll give you that. I don't recall claiming anyone dreamed of doing a shoulder roll to shoot a terrorist, but given my sarcastic nature, I can't say I've never thought it. I just think it's funny that the gun crowd doesn't tend to have people who are casually interested in the subject. Seems to be all or nothing. It is usually people who are obsessive about every single detail. Just an observation. It's not an insult, just more of a "here we go again" type of statement.

    There are people on this forum into cars, yet we don't have 10 threads a week talking about every single detail of every single detail about the subject of cars. Same for woodworking, underwater basket weaving, or any of the endless number of things people are interested in. For some reason I've never figured out, guns seem to connect to people in a different way than any other subject I can think of. As I've said before, I'm a pro gun guy. But I always feel like an outsider in the gun crowd since my zeal for the subject isn't at 110% all the time like many others seems to be.

    Anyways, if panties have been bunched, I will avoid the gun threads from now on.
     
    FennRx likes this.
  6. FennRx

    FennRx Senior Member

    Messages:
    17,253
    Likes Received:
    27,630
    Joined:
    Feb 21, 2008
    The correct answer is always 1/7 because muh military.

    :laugh2:
     
  7. FennRx

    FennRx Senior Member

    Messages:
    17,253
    Likes Received:
    27,630
    Joined:
    Feb 21, 2008
    I'd imagine a lot (most?) here consider me a so called gun nut (or just a nut).

    And you ain't wrong
     
    PeteK likes this.
  8. Who

    Who Who is not here. Please leave a message.... Premium Member

    Messages:
    13,120
    Likes Received:
    20,562
    Joined:
    Mar 15, 2012
  9. SteveC

    SteveC Get off my f*cking lawn. V.I.P. Member

    Messages:
    6,815
    Likes Received:
    11,764
    Joined:
    Apr 8, 2012
    In a 3-gun match, it's almost always an AR for the rifle stages. I have never seen any other type of rifle used in that competition.

    For a Practical Rifle match, there are always other types of rifles used. In fact, some matches specify the type of rifle (or, he genre) that you MUST use. For example, the WW-II match requires the use of a rifle that was used in combat - in any army. We get a lot of M1 Garands for this one. We also have an AK only match and an Iron-Sights-Bolt-Only match, too.

    In a Bullseye match, almost NO ONE shoots an AR. They are just not accurate enough to win, even with a professional shooter at the trigger. I shoot my AR, because I don't own any bolt actions, which is universally the rifle of choice.
     
  10. Frogfur

    Frogfur Senior Member

    Messages:
    12,660
    Likes Received:
    18,192
    Joined:
    Jan 18, 2013
    We are speaking of r
    This is exactly why I listen to guys like Rob here and Lt. when they talk. These folks know firearms and military subjects better than anyone on here. Including me. You want to pay attention to what they say. The above is no bull, and straight up advice and history.
     
  11. bulletproof

    bulletproof aka tarddoggy Premium Member V.I.P. Member

    Messages:
    6,669
    Likes Received:
    10,643
    Joined:
    Jun 1, 2011
    1:9....I do like the 62 grain greens. For me,they have just always worked very well. The ole Bush Master that I tend to favor(yup,its based around the A3) likes'em quite a bit. For me,personally,the BM is my close to the house type patrol weapon.I havent had a coyote get a chicken in quite awhile. However, Ive always been drawn to the 7.62/.308 for my all around,friend maker. Here lately,this here weapon has made my day. While I dont have the pretty green furniture on mine,they are identical......


     
  12. smk506

    smk506 Senior Member

    Messages:
    1,560
    Likes Received:
    1,725
    Joined:
    Jan 5, 2009

    To be fair Rob, I WAS touching myself a little reading your analysis. :eek2: :fingersx: :D
     
    Scooter2112, Roberteaux, Who and 3 others like this.
  13. Frogfur

    Frogfur Senior Member

    Messages:
    12,660
    Likes Received:
    18,192
    Joined:
    Jan 18, 2013
    20170704_122034.jpg
    Above are the green tips and below them xm193 ball. I like the green tips if I had to defend against animals due to the steel core.
    If they make contact with bone, something has to give. On any soft target, the 193 ball are just going to produce horrific wounds.
    The primary reason I carry the green tips in the woods, and would be inclined to use the 193 ball in other scenarios, sometimes soft points. Very mission specific really.

    Accuracy is everything discussed, proper barrels shooting cartridges with exceptional Ballistic coifficents, twist rates that compliment the type of shooting anticipated at ranges within capabilities of cartridge/barrel combinations that work, good load density, and attention to detail will get you there if you do your part.

    The thing is, no matter how good your weapon is, you cannot be proficient unless you shoot regularly, so don't BS us about your ability unless you are an active shooter.

    When you reload, shoot over a chronograph.
    If you don't, no matter what the books says everything being equal..you don't know.
    But if you do know velocities your producing, that can go along long way in load development. I got allot of information about that from Steve Herrett.
     
    Last edited: Jul 4, 2017
  14. LtDave32

    LtDave32 Sua Sponte Super Mod Premium Member

    Messages:
    25,920
    Likes Received:
    71,593
    Joined:
    Mar 19, 2010
    Not even close, froggy. I've been out of the reloading and AR lore for a long time. And All I ever reloaded was tons of handgun ammo.

    In the service, we did exactly -zero- monkeying with AR platforms. Strippin' ''em down, sure. But none of it was long-range accuracy stuff. Except for the M21 team attached to my unit. But that was them, not me. Though curious and interested, I was never an armorer. Those are the boys that know the platform inside and out. Along with ex-mil such as yourself who've tinkered with the platform a while, and who've made a lifelong hobby out of it. I defer all knowledge and expertise to fellas like you.
     
    Kris Ford, Roberteaux and bulletproof like this.
  15. LtDave32

    LtDave32 Sua Sponte Super Mod Premium Member

    Messages:
    25,920
    Likes Received:
    71,593
    Joined:
    Mar 19, 2010
    So, stay out of the damn thread if you don't like it.

    -And I'm not going to tell you again.

    Nobody's bothering you, and up until YOUR crap, we've been having a very civil and informative discussion.

    Next time you come into one of these threads to crap on the rest of us, action will be taken.

    Edit: just read the rest of your crap, and could not help but notice the "panties bunched" parting shot from you.

    Think that smart-assed comment was a big "win" for you?

    All you managed to do was to tick off the staff and the other members here having a peaceful, informative discussion, and YOU are the one looking like an ass for your efforts.
     
    Last edited: Jul 4, 2017
  16. LtDave32

    LtDave32 Sua Sponte Super Mod Premium Member

    Messages:
    25,920
    Likes Received:
    71,593
    Joined:
    Mar 19, 2010
    Rob, Froggy, GREAT info you've given. Thanks boys!
     
    Frogfur, Roberteaux and bulletproof like this.
  17. LtDave32

    LtDave32 Sua Sponte Super Mod Premium Member

    Messages:
    25,920
    Likes Received:
    71,593
    Joined:
    Mar 19, 2010
    Handled plenty of old G3's, including some of the really old ones with the wood furniture. Excellent rifle and design.
     
    Roberteaux, bulletproof and Frogfur like this.
  18. wizard1183

    wizard1183 Premium Member

    Messages:
    3,474
    Likes Received:
    1,747
    Joined:
    Sep 19, 2012
    That's one thing I'm missing is achronograph. But for now I'm just trying to get1/2"-3/4 moa with a scar17. Im down to 1 but I can get 1 with factory ammo. Reloading with Ramtac but I hate to buy varget right now. Only bought a lb so once I run out I'll go with pellet. I got up to 43gr and group was beginning to get tighter but I've heard most guys hitting around 42gr. The bench was uncomfortable so I may have screwed it up not knowing. I'm going to go back down to 41.8-42.8 and see.
     
    bulletproof likes this.
  19. Frogfur

    Frogfur Senior Member

    Messages:
    12,660
    Likes Received:
    18,192
    Joined:
    Jan 18, 2013
    That's good. But the only thing i need is how fast that bullet is going out of the tube. From there, I can figure out precisely what that cartridge is capable of.
    Loading books can be conservative sometimes. But if you know the components of the cartridge, such as case, primer, bullet type etc and velocity, all you need the book for is starting load data.

    You work up from there for optimum load density with powders that will give the best combination of burn rate/load density for a particular cartridge barrel combination and accuracy.

    The reason the barrel twist rate is so important is that, anything behind the barrel, except the trigger group (adjustable)is for housing the ammunition, and firing the projectile. It's the barrel that makes accuracy come true. If you can't send your round down range accurately, you can still scare hell out of them with rounds zoning everywhere.
    Know your velocity. A steady diet of full house loads is hard on your weapon.
     
    Roberteaux and bulletproof like this.
  20. wizard1183

    wizard1183 Premium Member

    Messages:
    3,474
    Likes Received:
    1,747
    Joined:
    Sep 19, 2012
    Well without a chrono I don't know how fast the bullet is coming out? I do know at 42gr? It's not as loud as 43! You can tell it's hot! My bro is the reloader and wants to go up to 44.( but I told him let's start over. Most avg 42gr so I don't want to go too high and break smtg.

    Ramshot TAC is ball powder. Supposedly half of temp of what military uses so they use it. But ball powder is inconsistent OR very finicky meaning it's at one point and then starts expanding. Now I'm not saying 43.2-44.5 won't produce an excellent group? But I rather try for a lower gr. before I start shooting way too hot.

    I know it's capable of 1/2" moa. And I can do it. I just need it to get there. And not t mention need to get much more comfortable. The bench is probably 36-40" high. They have steel chairs much more lower than comfortability. I have to sit on my legs. I'll get there though.

    I want it that way (1/2") so that I can shoot 300-500 yards consistently. I rarely shoot. However my bro is an avid deer hunter and he reloaded his and I got his down too 1/2" (3shot group) where as he can't do it. And that wasn't even afjusting the scope for me! Blurry as hell and I managed to pull it off. I have a leopold MK4 on the scar. It's good enough. Eventually I'm going to move to a FFP us optics or nightforce
     
    Last edited: Jul 4, 2017
    bulletproof likes this.

Share This Page