Hi All. I know the greater twist rate is designed to allow heavier bullets to be more accurate at long range (at least that is my layman's understanding). My question is does this in any way adversely affect lighter varmint weight bullets? I am talking about .223/5.56. Thank you.
1:7 twist and different bullets
- Thread starter baddarryl
- Start date
The faster twist spins the bullet faster at a given muzzle velocity. Heavier bullets in a given caliber tend to be longer and the longer the bullet, the faster it must be spun to stabilize it.
It is generally accepted that a faster twist barrel will wear faster, but it's not easy to quantify how much faster it will wear.
In addition, if you fire very light bullets at high velocity in a fast twist barrel, you can get bullet failures from excessive spin. The bullet can literally be torn apart by centrifugal force. That's kind of an extreme case, but it does happen.
You can also experience something called overstabilization if a bullet is spun a lot faster than is actually required to stabilize it.
Overstabilization becomes more of a problem as the range stretches. What happens is that the bullet is spinning so fast that it resists changing orientation to follow the arc of the trajectory. We know that the bullet follows an arc--it starts out aimed upwards a little bit, then at midrange it levels out and then it starts back down toward the ground as gravity pulls it downward.
A properly stabilized bullet will point in the direction of travel--there's enough spin to keep it generally oriented correctly but not so much gyroscopic force that the air resistance can't keep the nose pointed in the direction the bullet is actually going. So the bullet points up when the bullet is going up on the first part of the trajectory, level when it's level briefly at midrange, and down when the bullet starts back down. The spin/gyroscopic force keeps the bullet from tumbling and the air resistance keeps the nose pointing in the direction of travel.
If the bullet is overstabilized there's so much gyroscopic force that it won't allow air resistance to re-orient the bullet as it travels its arc. That means that the bullet is now not as efficient a projectile as it should be since it eventually ends up being pointed a little bit away from the direction it's actually travelling. If it starts out pointing a little bit up, it stays pointing in that direction all the way to the target. Obviously during the level and downward parts of the arc, the improper orientation increases air resistance and decreases the ballistic coefficient of the bullet.
It is generally accepted that a faster twist barrel will wear faster, but it's not easy to quantify how much faster it will wear.
In addition, if you fire very light bullets at high velocity in a fast twist barrel, you can get bullet failures from excessive spin. The bullet can literally be torn apart by centrifugal force. That's kind of an extreme case, but it does happen.
You can also experience something called overstabilization if a bullet is spun a lot faster than is actually required to stabilize it.
Overstabilization becomes more of a problem as the range stretches. What happens is that the bullet is spinning so fast that it resists changing orientation to follow the arc of the trajectory. We know that the bullet follows an arc--it starts out aimed upwards a little bit, then at midrange it levels out and then it starts back down toward the ground as gravity pulls it downward.
A properly stabilized bullet will point in the direction of travel--there's enough spin to keep it generally oriented correctly but not so much gyroscopic force that the air resistance can't keep the nose pointed in the direction the bullet is actually going. So the bullet points up when the bullet is going up on the first part of the trajectory, level when it's level briefly at midrange, and down when the bullet starts back down. The spin/gyroscopic force keeps the bullet from tumbling and the air resistance keeps the nose pointing in the direction of travel.
If the bullet is overstabilized there's so much gyroscopic force that it won't allow air resistance to re-orient the bullet as it travels its arc. That means that the bullet is now not as efficient a projectile as it should be since it eventually ends up being pointed a little bit away from the direction it's actually travelling. If it starts out pointing a little bit up, it stays pointing in that direction all the way to the target. Obviously during the level and downward parts of the arc, the improper orientation increases air resistance and decreases the ballistic coefficient of the bullet.
Wow, that was a mouthful! Thank you. I am specifically asking because I am thinking of getting a Colt AR with a 1:7 twist. All I will ever use it for is range time, a little varmint hunting, and if the shtf! Likely it will be my only one for a while so I am wondering if it will shoot the lighter loads accurately.
Scharfschuetzer
New member
Well said John.
When the first A2s came out with their 1 in 7 in twists, a lot of guys were still shooting 52 grain Match Kings at the 200 yard stages of the NM course. The thinking was that the higher velocity would help mitigate the shooter's wobble with a faster barrel time while in the standing position. It was not uncomon to see little bluish puffs of smoke between those shooters and the target. When they called for their target to be scored, it went down and then came up Maggie's Drawers.
When I shot Palma matches and the 7.62 NATO was still the required calibre, many shooters had special Palma rifles built with 1 in 14 twist barrels for the Sierra 155 grain Palma bullet. As John said, the thinking was that the bullet with the slower rate of twist would stay point on to its trajectory out at 800, 900 and 1,000 yards.
Do a google search for the "Greenhill Formula." It is a fairly good predictor of what twist is best for calibre and bullet weight in rifles.
With all that said, I have no trouble using 52 and 53 grain MKs in my personal HBAR. I will say though, that the overstabilization will cause groups to really open up with less then concentric or uniform bullets. With good bullets it will work fine for you and I shoot either the old 56 grain load or the 62 grain loads with equal aplomb in my 1 in 7" twist barrel. If you decide to shoot at long range, you can load up to 90 grain bullets and stabalize them even out at 1,000 yards with the 1 in 7 barrel.
A bit of minutia: The M-16A2 came out with the 1 in 7 twist not because the new 62 grain green tip ammo needed it. The green tip will shoot well in a 1 in 9 twist. The requirement for the 1 in 7 inch twist was due to the long tracer needed to hold enough phosphorous to burn to the military's requirement of 900 meters.
In 1986, I was in a South Asian country training with their troops on an exchange program. I had a lot of green tip ammo for my spanking new M-16A2, but the troops were armed with rather worn out M-16A1s and didn't have a lot of ammo. We tried the new green tip 62 grain bullets in the M-16A1s with their 1 in 12" twist and the projectiles were actually keyholing at 25 meters on the zero targets. Needless to say, we found something else to do until we got the older M 196 56 grain loads in.
When the first A2s came out with their 1 in 7 in twists, a lot of guys were still shooting 52 grain Match Kings at the 200 yard stages of the NM course. The thinking was that the higher velocity would help mitigate the shooter's wobble with a faster barrel time while in the standing position. It was not uncomon to see little bluish puffs of smoke between those shooters and the target. When they called for their target to be scored, it went down and then came up Maggie's Drawers.
When I shot Palma matches and the 7.62 NATO was still the required calibre, many shooters had special Palma rifles built with 1 in 14 twist barrels for the Sierra 155 grain Palma bullet. As John said, the thinking was that the bullet with the slower rate of twist would stay point on to its trajectory out at 800, 900 and 1,000 yards.
Do a google search for the "Greenhill Formula." It is a fairly good predictor of what twist is best for calibre and bullet weight in rifles.
With all that said, I have no trouble using 52 and 53 grain MKs in my personal HBAR. I will say though, that the overstabilization will cause groups to really open up with less then concentric or uniform bullets. With good bullets it will work fine for you and I shoot either the old 56 grain load or the 62 grain loads with equal aplomb in my 1 in 7" twist barrel. If you decide to shoot at long range, you can load up to 90 grain bullets and stabalize them even out at 1,000 yards with the 1 in 7 barrel.
A bit of minutia: The M-16A2 came out with the 1 in 7 twist not because the new 62 grain green tip ammo needed it. The green tip will shoot well in a 1 in 9 twist. The requirement for the 1 in 7 inch twist was due to the long tracer needed to hold enough phosphorous to burn to the military's requirement of 900 meters.
In 1986, I was in a South Asian country training with their troops on an exchange program. I had a lot of green tip ammo for my spanking new M-16A2, but the troops were armed with rather worn out M-16A1s and didn't have a lot of ammo. We tried the new green tip 62 grain bullets in the M-16A1s with their 1 in 12" twist and the projectiles were actually keyholing at 25 meters on the zero targets. Needless to say, we found something else to do until we got the older M 196 56 grain loads in.
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I doubt you'll have any problems.
That said, I have to ask, is there a specific reason you're looking at getting an AR with a fast twist barrel? Unless you are planning to shoot long-range target and/or have some reason to be shooting heavy/long for caliber bullets, 1:7 twist isn't really required.
I decided to move from a 30 cal to a AR several years back for shooting High Power. The wisdom at that time was you needed a fast twist to stabilize the 90 gr. Bullets which were coming out for 223. Based on the information given to me by well-known HP shooters I decided to go with a 6 ½ to 1 twist. Pac Nor had built some 6 ½ barrels and White Oak Precision had some of these barrels in stock. I commissioned WOP to build an AR with the 6 ½ with the idea of going out to 1K with my AR. I even have some cute Berger 90 gr. VLK’s. But I never put the two together. I did find out though this rifle gobbled up 77 and 80 gr. SMK’s like a house on fire. My scores sky rocketed.
In 2007 I figured out the 6 ½ was getting a few to many rounds on it to go to Perry so, I again commissioned WOP for another upper but using a 7 to 1 Krieger to make sure the 80 gr. SMK’s would stabilize for 600 yards. The Krieger shoots the 777 and 80 gr. SMK’s like a house on fire too. The 6 ½ became my second/loaner/practice/reduced match rifle to save the Krieger for full distance matches.
I have used the 52 and 53 gr. SMK’s at 100 yard reduced matches and have shot these pretty well. I have yet to have a bullet blow upon me. I have seen this on 168 SMK’s though and I know what it is. Bottom line for me is the 6 ½ twist has won me money and matches.
in the months and years which have passed since ordering the 61/2, we have figured found out a 7 to 1 will sabilize a 90 and an 80 can make to 1K.
In 2007 I figured out the 6 ½ was getting a few to many rounds on it to go to Perry so, I again commissioned WOP for another upper but using a 7 to 1 Krieger to make sure the 80 gr. SMK’s would stabilize for 600 yards. The Krieger shoots the 777 and 80 gr. SMK’s like a house on fire too. The 6 ½ became my second/loaner/practice/reduced match rifle to save the Krieger for full distance matches.
I have used the 52 and 53 gr. SMK’s at 100 yard reduced matches and have shot these pretty well. I have yet to have a bullet blow upon me. I have seen this on 168 SMK’s though and I know what it is. Bottom line for me is the 6 ½ twist has won me money and matches.
in the months and years which have passed since ordering the 61/2, we have figured found out a 7 to 1 will sabilize a 90 and an 80 can make to 1K.
handlerer2
New member
According to the Speer manual, a bullet exiting at 3500fps, from 1:7 barrel is revolving at 330,000rpm. This is enough centripetal force to stip the jackets from some varmint bullets.
Poodleshooter
New member
1x9" is a good all purpose twist from 40-75grs.
If you plan to shoot mostly 62-90gr bullets, use a 1x7" twist.
If you plan to shoot 35-55gr varmint bullets, 1x12" is a good choice.
Find your use for .223 and buy accordingly.
I spend time zapping small vermin and shooting reduced course of fire highpower with my .223, so the 75-90gr loads are of less value for me. I shoot them rarely in my 1x9s.
If you plan to shoot mostly 62-90gr bullets, use a 1x7" twist.
If you plan to shoot 35-55gr varmint bullets, 1x12" is a good choice.
Find your use for .223 and buy accordingly.
I spend time zapping small vermin and shooting reduced course of fire highpower with my .223, so the 75-90gr loads are of less value for me. I shoot them rarely in my 1x9s.
While uncommon, it's not unheard of, especially from light bullets going really fast. One day in the early '80s We were playing with a .22-250 and the bullets weren't hitting the target at 100 yards. We'd see a gray "smudge" in the air and realized that the bullets were being overdriven and coming apart in flight. It had a lot of "wow" factor. I've never seen that in a .223, but I suspect that it might be possible.
I've owned several 223's all have been with 1/9 twist my best groups at 100yards came with the 52gr match bullets, with proper loads I expect those same bullets would do great in a 1/7 twist. Honestly I do not see the need for 1/7 twist for most shooters just depends on your requirements.
Several Reasons: The ability to use heavier bullets allows you to use the 223 varmint hunting in windy areas. Never saw a PD town where the wind didn't blow.
Heavy bullets extend the range of the 223.
223s are required in AR service rifle matches, not 6 MMs, to be competitive you're gonna have to shoot heavy bullets, light one's just wont cut it at 600 & 1000 yards.
In High Power Matches the ARs have allowed more ladies and younger shooters to be competitive then the M1A/M14s, that alone is a big selling point to me.
Many places allow 223s for deer hunting, the heavier bullets would be more effective on deer/antelope size animals.
I agree one rifle can't do it all, but if you are going to shoot a 223, why not go to a twist that will allow light and heavy bullets.
But the AR isn't "best" with 50 - 60 grn bullets, the AR is best if you can shoot 50-90 grn bullets where you can cover a wider spectrum of shooting with a 223 AR.
Plus, its cheaper to shoot 223s then ARs.
Poodleshooter
New member
I didn't elaborate on this earlier because I've done it ad nauseum on various forums, but I had a Colt 1x7" that would reliably blow up most hollow point varmint bullets under 55grs when shot at 3000fps or more, and showed signs of causing jacket breakdown with even Winchester 55gr FMJs at 3000fps using WC844 or WC846, and even with hefty Varget loads. You'd get a grey streak and sometimes a "puff" at about 75yds downrange, especially on sunny,hot days. The FMJs shot basketball sized patterns at 100yds, when a Hornady 68gr BTHP load would drill nice MOA groups at the same distance. Dropping velocity below 2900fps usually made the problem go away.
Sierra 52/53gr SMKs were a notable exception that still shot well at normal velocities from the 20" barrel.
For me, a guy who only shoots 100yd RCOF highpower, and can't even find a hunting situation beyond 300yds, that 1x7" was actually limiting. I didn't need anything over 75grs, but I did want the ability to shoot 40-50gr bullets very fast for varminting.
Sure, there's guys shooting 1x7s with reloads using Hornet weight bullets, but why take the chance if you don't need the 80-90gr single loaded bullets for the 600yd line?