I've owned 2 AR's with 1:8 barrels. A M&P15 Sport and a PSA 300BLK AR. Both were reasonably accurate for my uses.
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I've owned 2 AR's with 1:8 barrels. A M&P15 Sport and a PSA 300BLK AR. Both were reasonably accurate for my uses.
Personally think both are fine for a majority of shooters. I have ARs with 1/9, 1/8, and 1/7. The 1/7 is a BCM 16 inch BFH middy, the 1/8 is a RRA 20inch rifle. Benched, at 100 meters last time I had them out with the same ammo, 55gr Steel match, the 1/8 grouped about half the size of the BCM. However, it really means nothing in my opinion since the RRA was shot with a 9 power scope, and the BCM a 4 power ACOG. Also have grouped both rifles in the past and had the BCM group tighter than the RRA, though I was shooting really hot that day with the BCM. Personally I don't see myself going below 55gr and from my understanding 1/7 still stabilizes 70+ grain bullets plenty well enough for what I want to be able to do. That said, for the time being the RRA is going to stay, at least until I can prove that it is no more accurate than the BCM at which point I'll likely sell the upper and replace it with another BCM. Maybe a Centurion, or Rainier.
Another reason why I believe the 1/7 is the better twist, is the fact that it shoots not just heavy mag lenth loads....but the real .223 LR projectiles like the 80gr. smks, 80gr/90gr. Berger VLDs, and several others that are extensively used in .223 bolts.
Might not be very popular, but folks like myself who are distance junkies take advantage of having the perfect twist rate for shooting the vastly superior LR projectiles. I'm sure the 1/8 would shoot them fine, however those bullets were designed to be best used w/ 1/7 barrels.
http://www.youtube.com/watch?v=QaJLPihtFSI
Let's look at the extremes of .223 projectile sizes/weights, and their formulated preferred twist rate by comparing their gyroscopic stability factor (SG) .....
First set of charts are based on one of the heaviest projectiles made for .223, the 90gr. Berger VLD.
90gr. VLD
Chart 1: calculated w/ 1/7
http://i888.photobucket.com/albums/a...ps9d982cf6.jpg
Chart 2: calculated w/ 1/8
http://i888.photobucket.com/albums/a...ps02935453.jpg
Chart 3: calculated w/ 1/9
http://i888.photobucket.com/albums/a...pse7b96218.jpg
Now for the total opposite end of the spectrum...
52 gr. match FB
chart 1: calculated w/ 1/7
http://i888.photobucket.com/albums/a...ps0dfa4169.jpg
chart 2: calculated w/ 1/8
http://i888.photobucket.com/albums/a...psbcd29395.jpg
chart 3: calculated w/ 1/9
http://i888.photobucket.com/albums/a...ps6c8f431b.jpg
Ballistician wizard Bryan Litz recommends in his book Applied Ballistics For Long-Range Shooting that you aim for at least a 1.4 SG rating when selecting a barrel twist for a particular bullet. This gives you a safety margin for shooting under various conditions, such as higher or lower altitudes or temperatures. Try changing the altitude and Temperature in the calculator and you will see that the SG drastically changes. Under optimal circumstances you should aim for a 1.4, that way if you change circumstances you are still over 1.1.
These tight twist rates are for short barrels. If you have a 16 inch or longer barrel (which most people do) 1/9 will be fine for the ammo most people shoot (55 and 62grn.) You have to remember, even most of the "Spec Ops" guys are just young kids who don't know much. They go in using a 5.56x45 round--who's only advantage is velocity--and use SBR's or the Military uses a 14.5in. barrel because they think they need it (How SF/SOF ever got on before that time is amazing isn't it?) and it robs the cartridge of it's one advantage. So they spend all this time and effort to rob peter to pay paul and end up with crazy tight twist rates and really heavy grain bullets and it's mostly just nonsense. Civilians pick up on it because it looks cool and blah, blah, blah. The civilian 16in. barrel is a more optimal short barrel than the military has. You have a better gun than they do. Stick with 1/9 on a 16in. and don't sweat it. The guys who tell you otherwise are doing it to make money or because they don't know any better. K.I.S.S. it.
There's a reason why most of the SS Match barrels are 1/8 twist.
Also, it just so happens that one of the most accurate Chrome Lined barrels (arguably) is 1/8 twist.
You have no clue what you're talking about. Please refrain from spreading untruths and absolute falsehoods and read the stickies/this forum before posting more.
1/7 and 1/8 are not just for short barrels, and especially have uses in longer barrels for precision work using heavy OTM rounds. Modern 5.56 performs very well these days, even in 14.5" or lesser guns, and using short barrels doesn't rob the cartridge of anything in many uses. Faster twist rates aren't nonsense and have huge, measurable, objective advantages when using 75 and 77 grain loads, which many of us use these days. Civilians, especially on this board, use guns and barrels with these twist rates for their real-world performance, not because it looks cool.
16" barrels are more optimal? For what use? What ammo? What purposes? This claim makes no sense without qualifying information. Even with it, there is actually fairly little difference between 16 and 14.5 in performance. And finally, people who say not to choose 1/9 barrels do not do so to make a buck or because we're ignorant -- we do so because we know exactly what we're talking about and because we nigh-objectively know what will perform best for most people's uses, and that IS NOT 1/9.
You obviously are among the crowd of people who you say give bad advice because they don't know any better. You obviously don't know what you're talking about. You obviously need to educate yourself more on this subject before offering advice to people.
Please do so.
11th ACR LRRP, 3rd Squadron, 4th Troop, '68-'69. I dare say I know a little more about pragmatic usage of the AR than you do son. Don't be rude.
I'm not being rude. I'm being honest. You don't know what you're talking about and are giving bad advice. You need to read more. Your service doesn't give you any extra insight into the technical aspects of AR design and performance, especially in the year 2014, where technology is quite a bit different than 1969.