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woody78
09-20-2011, 6:59 AM
What does the number of twist mean in a .223 barrel? What is a good number to get? I've heard 1:16 is good but I couldn't find any barrels with that

coyotebait
09-20-2011, 7:43 AM
What does the number of twist mean in a .223 barrel? What is a good number to get? I've heard 1:16 is good but I couldn't find any barrels with that

1:16 would be 1 full twist in 16 inches. 1:8 would be 1 full twist in 8 inches. I'm not sure that they even make a 1:16 for the 223 but if they do I'd run from it. The tighter the twist, the heavier the bullet that it will shoot accurately.

melodybliss
09-20-2011, 7:45 AM
Also, if the twist rate is high, you will have issues shooting lighter ammunition. It'll twist the bullet too much and will have issues stabilizing.

What is it you want to shoot out of it?

Bhobbs
09-20-2011, 7:50 AM
1:16 would be 1 full twist in 16 inches. 1:8 would be 1 full twist in 8 inches. I'm not sure that they even make a 1:16 for the 223 but if they do I'd run from it. The tighter the twist, the heavier the bullet that it will shoot accurately.

That's not entirely true. The twist rate will be determined by what bullets you want to shoot and how long they are. The heavier bullets by design are longer and need to be spun faster to maintain the proper stability over their flight. You can have lighter bullets that need a faster twist depending on what they are made of. If they are made of less dense materials than lead, they will have to be made longer to get the same weight which would require the faster twist.

coyotebait
09-20-2011, 7:54 AM
That's not entirely true. The twist rate will be determined by what bullets you want to shoot and how long they are. The heavier bullets by design are longer and need to be spun faster to maintain the proper stability over their flight. You can have lighter bullets that need a faster twist depending on what they are made of. If they are made of less dense materials than lead, they will have to be made longer to get the same weight which would require the faster twist.

Correct, I just really didn't want to type all that.:43:

woody78
09-20-2011, 8:17 AM
Also, if the twist rate is high, you will have issues shooting lighter ammunition. It'll twist the bullet too much and will have issues stabilizing.

What is it you want to shoot out of it?

Im not sure on the ammo but I don't want nothing extremely expensive. Im still in the beginning stages of building my AR. So what is the average/good number if twist you should get?

Bhobbs
09-20-2011, 8:36 AM
Im not sure on the ammo but I don't want nothing extremely expensive. Im still in the beginning stages of building my AR. So what is the average/good number if twist you should get?

1:8 is a good overall twist rate.

CK_32
09-20-2011, 9:03 AM
1:8

Nathan Krynn
09-20-2011, 12:13 PM
1/16 is for 22lr. .223 is 1/9, 1/8, or 1/7.

Nathan

ejhc11
09-20-2011, 12:44 PM
If you want to shoot bullets over 70gr then get at least a barrel 1:8 or 1:7 otherwise a 1:9 barrel will be fine.

greent
09-20-2011, 1:04 PM
basically everyone's right. I just bought my first ar in 1:7. I have heard from numerous people who own the 1:7 barrels that they shoot the lighter ammo just fine. Look at online ammo dealers and there's a lot of heaver ammo that is still just as cheap as the light stuff. heavier ammo has better ballistics and more long range stability. The military uses 1:7 if that's worth anything to you.

AeroEngi
09-20-2011, 1:18 PM
That's not entirely true. The twist rate will be determined by what bullets you want to shoot and how long they are. The heavier bullets by design are longer and need to be spun faster to maintain the proper stability over their flight. You can have lighter bullets that need a faster twist depending on what they are made of. If they are made of less dense materials than lead, they will have to be made longer to get the same weight which would require the faster twist.

Actually, a heavier bullet needs less spin (rotational velocity) than a lighter bullet to remain stable. It's all about angular momentum. The heavier the bullet, the less spin you need to reach a stable angular momentum. The lighter the bullet, the more spin you'll need to reach a stable angular momentum. It's just harder to spin a heavier bullet, that's why you need the tighter barrel twist.

send it_hit
09-20-2011, 1:23 PM
i've shot 55 grain, 65 grain, 69 grain, 75 grain, 77 grain, and 80 grain out of my 1:8 barrel, and by far 77 grain grouped the best. I was surprised it mattered so much at 100yds but it sure did.

Go 1:8 or 1:7, buy a few different grains, and see what works best for you. But I'd bet somewhere between 70-80 grain.

motorwerks
09-20-2011, 1:26 PM
I've been going with 1:8 because it seems to be the best of both worlds for the shooting I do.

Vacaville
09-20-2011, 1:30 PM
The ideal twist rate depends on your application for the firearm.

I have a bolt-action .223 that has a 1:12 twist rate, which is pretty slow. It's a tack driver with 40 - 55 grain bullets. If I shoot anything over 60 grains or so, my accuracy decreases rapidly with the increased bullet weight. I use the rifle for punching tiny groups on paper, and small game. If you want to shoot larger predators, like mountain lions, you probably want a heavier bullet, and thus a faster twist rate. 1:8 or 1:9 are pretty standard all-around .223 twist rates.

Bhobbs
09-20-2011, 1:33 PM
Actually, a heavier bullet needs less spin (rotational velocity) than a lighter bullet to remain stable. It's all about angular momentum. The heavier the bullet, the less spin you need to reach a stable angular momentum. The lighter the bullet, the more spin you'll need to reach a stable angular momentum. It's just harder to spin a heavier bullet, that's why you need the tighter barrel twist.

I have to disagree. For that to be the case the bullet would slide over the lands of the rifling which would tear up the jacket. That does not happen. The bullet is forced into the grooves and is spun at the same rate.

The heavier bullet will maintain its rotation better due to it having a greater rotational momentum but that has nothing to do with the rifling twist needed to stabalize it.

AeroEngi
09-20-2011, 1:50 PM
I have to disagree. For that to be the case the bullet would slide over the lands of the rifling which would tear up the jacket. That does not happen. The bullet is forced into the grooves and is spun at the same rate.

The heavier bullet will maintain its rotation better due to it having a greater rotational momentum but that has nothing to do with the rifling twist needed to stabalize it.

So are you saying that for example, a 50 grain bullet and a 62 grain bullet will come out of the muzzle of a 1:7 twist rifle at the same spin rate? Assuming the 50 grain has a higher muzzle velocity than the 62 grain.

The heavier bullet will maintain it's rotation for a longer period of time because of it's moment of inertia.

Bhobbs
09-20-2011, 2:08 PM
So are you saying that for example, a 50 grain bullet and a 62 grain bullet will come out of the muzzle of a 1:7 twist rifle at the same spin rate? Assuming the 50 grain has a higher muzzle velocity than the 62 grain.

The heavier bullet will maintain it's rotation for a longer period of time because of it's moment of inertia.

The rpm won't be the same because the lighter bullet will be traveling faster but they will both rotate one complete turn in the same distance initially but it will change as the velocity drops off.

meltyman
09-20-2011, 2:11 PM
Hmm I hadn't thought of it that way before. Perhaps the resulting spin rate exiting the barrel is actually very similar for light vs heavy bullets, the heavier ones just need a higher twist rate to get there since they are travelling slower. Don't feel like math right now.

Bhobbs
09-20-2011, 2:20 PM
Hmm I hadn't thought of it that way before. Perhaps the resulting spin rate exiting the barrel is actually very similar for light vs heavy bullets, the heavier ones just need a higher twist rate to get there since they are travelling slower. Don't feel like math right now.

Lets say a 55 grain bullet has a MV of 3,200 fps out of a 1:9 twist.

12/9 = 1.33 rotations per foot.
The bullet flies at 3,200 fps so it would rotate 1.33*3,200 = 4,256 times per second.

RPM = 4,256*60 = 255,360 rpm.

A 90 grain bullet has a muzzle velocity of 2,700 fps out of a 1:7 twist.

12/7 = 1.71 rotations per foot.
The bullet flies at 2,700 fps so it would rotate 1.71*2,700 = 4,617 times per second.

RPM = 4,617*60 = 277,020 rpm.

AeroEngi
09-20-2011, 2:27 PM
The rpm won't be the same because the lighter bullet will be traveling faster but they will both rotate one complete turn in the same distance initially but it will change as the velocity drops off.

I have to disagree man. Even when 5 inches down the barrel, the lighter bullet will have a higher spin rate because it has traveled down those 5 inches in less time than the heavier bullet, eventually coming out of the muzzle at a higher RPM than the heavier bullet.

Now if they have the same muzzle velocity, then that's a completely different story.

Hmm I hadn't thought of it that way before. Perhaps the resulting spin rate exiting the barrel is actually very similar for light vs heavy bullets, the heavier ones just need a higher twist rate to get there since they are travelling slower. Don't feel like math right now.

I did the math LOL. That's why you need a slower twist rate for the lighter bullets. Regardless of bullet size and weight, both the lighter and heavier bullets need approximately the same angular momentum to become "stable". Because the lighter bullet lacks weight, it needs more spin (RPM) and vice versa for the heavier bullet. You can have a 62 grain coming out of a 1:7 barrel have the same RPM as a 50 grain coming out of a 1:8 or 1:9 barrel. Say for example, if the 50 grain and 62 grain bullets had the same muzzle velocity and assuming the 50 grain is perfectly stabilized, then the 62 grain would be over-stabilized. In this situation, you would need a slower twist rate for the heavier bullet to reach the same angular momentum as the lighter bullet but most of the time, the lighter bullet would have the higher muzzle velocity. Makes sense?

Mute
09-20-2011, 2:28 PM
So are you saying that for example, a 50 grain bullet and a 62 grain bullet will come out of the muzzle of a 1:7 twist rifle at the same spin rate? Assuming the 50 grain has a higher muzzle velocity than the 62 grain.

The heavier bullet will maintain it's rotation for a longer period of time because of it's moment of inertia.

The weight is irrelevant. If the two bullets are the same length, the twist rate will suffice for both. Take a look at the Greenhill Formula which is most often used to determine the correct twist rate for a given bullet. Weight is not used in the calculation.

AeroEngi
09-20-2011, 2:29 PM
Lets say a 55 grain bullet has a MV of 3,200 fps out of a 1:9 twist.

12/9 = 1.33 rotations per foot.
The bullet flies at 3,200 fps so it would rotate 1.33*3,200 = 4,256 times per second.

RPM = 4,256*60 = 255,360 rpm.

A 90 grain bullet has a muzzle velocity of 2,700 fps out of a 1:7 twist.

12/7 = 1.71 rotations per foot.
The bullet flies at 2,700 fps so it would rotate 1.71*2,700 = 4,617 times per second.

RPM = 4,617*60 = 277,020 rpm.

Your math-fu looks correct LOL :)

AeroEngi
09-20-2011, 2:30 PM
The weight is irrelevant. If the two bullets are the same length, the twist rate will suffice for both.

The weight is very relevant. The twist rate may suffice for both but one may be slightly over-stabilized and the other may be perfectly stabilized.

Bhobbs
09-20-2011, 3:39 PM
The weight is very relevant. The twist rate may suffice for both but one may be slightly over-stabilized and the other may be perfectly stabilized.

If light for caliber bullets require a faster twist, why do pistol bullets have extremely slow twists rates at their slower muzzle velocity?

AeroEngi
09-20-2011, 3:55 PM
If light for caliber bullets require a faster twist, why do pistol bullets have extremely slow twists rates at their slower muzzle velocity?

For .45 ACP, a 230 grain bullet requires a 1:16 twist rate. 9 mm requires a 1:10 twist rate. You can't really compare rifles to pistols in this way because the bullets from rifles experience more "twisting" due to their longer barrels. This has nothing to do with pistols but the 50 BMG (which is relatively heavy) has a common twist rate of 1:15. Why does an AR-15 in 5.56 have a faster barrel twist than a 50 BMG?

Bhobbs
09-20-2011, 4:40 PM
For .45 ACP, a 230 grain bullet requires a 1:16 twist rate. 9 mm requires a 1:10 twist rate. You can't really compare rifles to pistols in this way because the bullets from rifles experience more "twisting" due to their longer barrels. This has nothing to do with pistols but the 50 BMG (which is relatively heavy) has a common twist rate of 1:15. Why does an AR-15 in 5.56 have a faster barrel twist than a 50 BMG?

Probably because the length to diameter ratio of the heavy .223 bullets is greater than the ratio for the .510 bullets.

Phil3
09-20-2011, 9:19 PM
I would generally go with twist rates shown at www.6mmbr.com. Thos guy s know accuracy. For my short range shooting with flat based bullets (work well at short range), a 1:12 is good for a 223. My AR15 223 uses 1:9 and will shoot small groups with 55 grain bullets. 69 grain did not improve anything, and may have been worse, despite the higher quality ammo.

- Phil

dieselpower
09-20-2011, 9:27 PM
I made this and have posted it here before. Its not a bible by any means, just a visual chart so people can understand the twist/weight thing a little better. Some people just need to see a graph. sorry for the grammar errors...it was a rush job.

http://i655.photobucket.com/albums/uu272/Wiringguy/223and556twistgraphed.png

captbilly
09-20-2011, 11:02 PM
I am a physicist and engineer and I have done a bit of research on the physics of stabilizing a bulle. Here is what I have found: There is definitely a minimum twist rate required to stabilize a bullet. Basically only one factor enters into the calculation of minimum twist rate for stability, the diameter squared divided by the length of the bullet. In reality it is a bit more complex because the mass distribution of bullets is not tthe same between different profiles of bullet (flat base round nose vs. boat tail hollow point, vs. wad cutter, etc.) and lower density bullets will not need as fast a twist as a same length and profile denser bullet (a brass bullet of the same length as a tungsten bullet will only need a slower twist). Most of the people who have developed the various formulas for calculating twist rate suggest that you can go about 50% faster then necessary in twist rate without any issues, which would mean that if a 1 in 9 barrel were the minimum required for stability for a particular bullet, you could've go to 1 in 6 without issue. But what happens if you do go to an overstabilized twist rate? The main issues seem to be excessive barrel wear (compared to what you would get with a slower twist barrel), the possibility of throwing a jacket (not dangerous but it will ruin the shot), and finally a possibility of poor accuracy.

Let me explain what I mean about a possibility of poor accuracy. If the bullet is not perfectly balanced then when it leaves the barrel it will veer slightly off of bore. Solid bullets that are machined on a lathe will not show much of this effect (assuming they ride straight down the barrel), but a poorly made jacketed bullet can. But this effect is evident in all barrels, it simply increases with spin rate, and the effect is generally very very small, almost insignificant for all but the benchrest guys. I once calculated that the entire inaccuracy caused by imbalance in my 1 in 10 .308 rifle, when shooting a pretty badly balance bullet, was about 0.1 moa. So if I shot that same bullet out of a 1 in 8 barrel the inaccuracy would increase to perhaps a whopping., 0.15 moa, or a difference of 0.05 moa. The bench rest guys care about 0.05 moa but for an aR that shoots 0.5 moa with match ammo and a great shooter, 0.05 moa is virtually meaningless. The bottom line is that there is no such thing as overstabilized, but poorly balanced bullets will contribute more and more error, although still small for any decent bullet, as the bullet spins faster (but will always contribute to inaccuracy at any twist rate). The error is not due to excessive stability, but because the bullet is forced sideways as it leaces the barrel

freonr22
09-20-2011, 11:12 PM
how long does it take bullets to reach "their" terminal velocity?

dieselpower
09-21-2011, 6:07 AM
I am a physicist and engineer and I have done a bit of research on the physics of stabilizing a bulle. Here is what I have found: There is definitely a minimum twist rate required to stabilize a bullet. Basically only one factor enters into the calculation of minimum twist rate for stability, the diameter squared divided by the length of the bullet. In reality it is a bit more complex because the mass distribution of bullets is not tthe same between different profiles of bullet (flat base round nose vs. boat tail hollow point, vs. wad cutter, etc.) and lower density bullets will not need as fast a twist as a same length and profile denser bullet (a brass bullet of the same length as a tungsten bullet will only need a slower twist). Most of the people who have developed the various formulas for calculating twist rate suggest that you can go about 50% faster then necessary in twist rate without any issues, which would mean that if a 1 in 9 barrel were the minimum required for stability for a particular bullet, you could've go to 1 in 6 without issue. But what happens if you do go to an overstabilized twist rate? The main issues seem to be excessive barrel wear (compared to what you would get with a slower twist barrel), the possibility of throwing a jacket (not dangerous but it will ruin the shot), and finally a possibility of poor accuracy.

Let me explain what I mean about a possibility of poor accuracy. If the bullet is not perfectly balanced then when it leaves the barrel it will veer slightly off of bore. Solid bullets that are machined on a lathe will not show much of this effect (assuming they ride straight down the barrel), but a poorly made jacketed bullet can. But this effect is evident in all barrels, it simply increases with spin rate, and the effect is generally very very small, almost insignificant for all but the benchrest guys. I once calculated that the entire inaccuracy caused by imbalance in my 1 in 10 .308 rifle, when shooting a pretty badly balance bullet, was about 0.1 moa. So if I shot that same bullet out of a 1 in 8 barrel the inaccuracy would increase to perhaps a whopping., 0.15 moa, or a difference of 0.05 moa. The bench rest guys care about 0.05 moa but for an aR that shoots 0.5 moa with match ammo and a great shooter, 0.05 moa is virtually meaningless. The bottom line is that there is no such thing as overstabilized, but poorly balanced bullets will contribute more and more error, although still small for any decent bullet, as the bullet spins faster (but will always contribute to inaccuracy at any twist rate). The error is not due to excessive stability, but because the bullet is forced sideways as it leaces the barrel

I get that you did the whole math thing and that you are a very smart person. Heres the deal. Real life doesn't add up to your science.

If I take a 77gr MK262 and fire it at a 10" target 375 yards away, I will miss the target completely most of the time. If I take a 62gr M855 and do the same, (re-zeroing at 25 yards for the cross zero at 375 yards mind you), I will hit more often than not. If I (for the third time) re-zero using 55gr M193 I will hit a majority of the time. I use a 1:9 twist.

Now bring that range into my comfort zone of 200 yards.... all ammo is about the same. That extra 175 yards makes that twist more critical in the accuracy of the ammo. I hear the same can be said the other way as well. A M193 or M855 shot out of a 1:7 isn't as accurate at long range as a MK262 is. This is why the Government is going with 1:8 for the SPR. The error at both ends is diminished considerably.

Its also not only about accuracy. A projectiles destructive potential against living tissue is altered as well with different twist. A MK262 shot from a 1:9 at a target 400 yards away doesn't have the lethality it does when shot from a 1:7 at that same range. Once again bring that target closer and its fine. So I and many others sacrifice accuracy at longer ranges and lethality at longer ranges for the ability to use shorter ammo and still maintain lethality and accuracy with that 55gr ammo. Another factor is I would never as a civilian engage a threat 400 yards away for any reason with a AR15...thats what the 308, 7.62x51 (or 54) is for ;)

Metal Magic
09-21-2011, 8:53 AM
That chart is really helpful. I'm tagging this thread for future reference. :thumbsup:

AeroEngi
09-21-2011, 9:44 AM
I get that you did the whole math thing and that you are a very smart person. Heres the deal. Real life doesn't add up to your science.
If I take a 77gr MK262 and fire it at a 10" target 375 yards away, I will miss the target completely most of the time. If I take a 62gr M855 and do the same, (re-zeroing at 25 yards for the cross zero at 375 yards mind you), I will hit more often than not. If I (for the third time) re-zero using 55gr M193 I will hit a majority of the time. I use a 1:9 twist.

Now bring that range into my comfort zone of 200 yards.... all ammo is about the same. That extra 175 yards makes that twist more critical in the accuracy of the ammo. I hear the same can be said the other way as well. A M193 or M855 shot out of a 1:7 isn't as accurate at long range as a MK262 is. This is why the Government is going with 1:8 for the SPR. The error at both ends is diminished considerably.

Its also not only about accuracy. A projectiles destructive potential against living tissue is altered as well with different twist. A MK262 shot from a 1:9 at a target 400 yards away doesn't have the lethality it does when shot from a 1:7 at that same range. Once again bring that target closer and its fine. So I and many others sacrifice accuracy at longer ranges and lethality at longer ranges for the ability to use shorter ammo and still maintain lethality and accuracy with that 55gr ammo. Another factor is I would never as a civilian engage a threat 400 yards away for any reason with a AR15...thats what the 308, 7.62x51 (or 54) is for ;)

Why do you say that?

The chart you posted...is that based on some calculations or just from what you've observed?

dieselpower
09-21-2011, 4:18 PM
Why do you say that?

The chart you posted...is that based on some calculations or just from what you've observed?

i said that since his general post was that it didnt really matter, when on paper he is correct, but in actual shooting it does.

its based off of known balistics of the ammo and twists. many believe 1:7 is the best overall since the military uses that. for the military cannon fodder grunt 1:7 is the best. for specialized advanced marksmen 1:8 is the best. as a civilian its a personal choice on what twist based on what ammo supply you have. range and type of target factor as well.

AeroEngi
09-21-2011, 4:39 PM
i said that since his general post was that it didnt really matter, when on paper he is correct, but in actual shooting it does.

its based off of known balistics of the ammo and twists. many believe 1:7 is the best overall since the military uses that. for the military cannon fodder grunt 1:7 is the best. for specialized advanced marksmen 1:8 is the best. as a civilian its a personal choice on what twist based on what ammo supply you have. range and type of target factor as well.

As an engineer, I do have to admit that using science to predict real life is extremely difficult but it gives us a better understanding with what's really going on. Everything follows the laws of physics, bullets included. The reason why we know that a 1:7 twist is optimal for bullet weights of 62 grains and above is because at one point, someone actually ran the numbers and predicted it before a 62 grain bullet was ever fired out of a 1:7 twist barrel. Why do you think all these bullets that we speak of are shaped the way they are? You may think science is only good on paper but I highly and respectfully disagree.

Fjold
09-21-2011, 5:49 PM
You people need to stop saying "weight" when it comes to discussions about twist.

phish
09-21-2011, 6:03 PM
You people need to stop saying "weight" when it comes to discussions about twist.

no kidding, mention 75 or 77 gr. bullets and it's "1:7 or gtfo"

dieselpower
09-21-2011, 6:21 PM
You people need to stop saying "weight" when it comes to discussions about twist.

would you prefer "length"?

as in, My 1:9 twist, 14.5" shoots 77gr length projectiles fine under 200 yards.

slick_711
09-21-2011, 6:30 PM
If you want to shoot bullets over 70gr then get at least a barrel 1:8 or 1:7 otherwise a 1:9 barrel will be fine.

Odd, my SPS Tactical (1:9) will put 5 rounds of 77gr SMK in a quarter all day long at 100yds. :rolleyes:

I would say 1:7 - 1:9 are fine, and different brand barrels will vary as to their exact twist rate (despite what they're marked) and what ammunition they may like best. The average shooter is never going to notice a difference as long as he goes with one of those three.

Mute
09-21-2011, 6:34 PM
You people need to stop saying "weight" when it comes to discussions about twist.

Ok...we'll use specific gravity.

UBFRAGD
09-21-2011, 7:32 PM
If I (for the third time) re-zero using 55gr M193 I will hit a majority of the time. I use a 1:9 twist.

I like this combo too.

grant22
09-25-2011, 8:42 PM
If I'm looking to do precision shooting at a range (100, 200, & 300 yards), am looking to get a new upper (20" bull barrel), have tons of my 55 gr reloads (can make heavier if needed), would you all suggest a 1:8? if I get a 1:8, would 55's do pretty well at least at 100 yds?

surfNshoot
09-27-2011, 12:16 PM
If I'm looking to do precision shooting at a range (100, 200, & 300 yards), am looking to get a new upper (20" bull barrel), have tons of my 55 gr reloads (can make heavier if needed), would you all suggest a 1:8? if I get a 1:8, would 55's do pretty well at least at 100 yds?

if you are going to do precision shooting. I highly suggest going with hevier 75gr or 77gr bullets. However, yes 55gr will shoot fine out of a 1:8 twist.

Richard Erichsen
09-27-2011, 2:35 PM
What does the number of twist mean in a .223 barrel? What is a good number to get? I've heard 1:16 is good but I couldn't find any barrels with that

Search is your friend. More has been said about this topic, particularly with regard to .223 but by no means limited to that caliber through umteen threads as a quick search for "barrel twist" or "rifling twist" proves.

Sikhawk
09-27-2011, 4:20 PM
to quote JT:

"It is a well documented fact that if you run 77 gr. bullets in a 9 twist barrel, the universe will cease to exist."

BIRDHUNTER757
09-27-2011, 7:58 PM
Actually, a heavier bullet needs less spin (rotational velocity) than a lighter bullet to remain stable. It's all about angular momentum. The heavier the bullet, the less spin you need to reach a stable angular momentum. The lighter the bullet, the more spin you'll need to reach a stable angular momentum. It's just harder to spin a heavier bullet, that's why you need the tighter barrel twist.

Not true. You have it backwards. Heavy faster twist, lighter slower twist.

Richard Erichsen
09-28-2011, 9:37 AM
Not true. You have it backwards. Heavy faster twist, lighter slower twist.

Correct, though one nit is that weight "usually" correlates to length, but not always. The fairly new lead-free copper projectiles can be very long for their mass compared to a lead core/copper jacketed slug. For that reason, the new craze in "lead free" super ammo may demand a faster twist to stabilize the longer bullets even though the weight of the bullet remains the same. Compare a lead core 62-70 grain copper (Corbon DPX or similar) to the lead core 62-70 grain SP and you'll note the length difference. What might be adequate if marginal with a lead core bullet may be inadequate and "key hole" with the copper rounds.

sapper911
09-28-2011, 1:30 PM
55Gr is the cheapest most common ammo. A barrel with a 1/9 is designed for 55gr.
So if i were you i would get sonething with a 1/9 twist.

surgical
10-08-2011, 1:52 PM
So if I were going for maximum range, what would be the best combo? Short twist with heavy bullet?

Bhobbs
10-08-2011, 2:13 PM
So if I were going for maximum range, what would be the best combo? Short twist with heavy bullet?

If you wanted the maximum range out of an AR15 I would run the 90 grain VLD loaded long with a 1/7 or faster twist and use a really long barrel. You will probably have to single load them as the OAL with be longer than the mag length.

dieselpower
10-08-2011, 7:15 PM
69gr 1:9 twist 1000 yards, Savage 11 in .223 Rem. 20" barrel
CCJxQqkgGf0

DPMS AR15, 1:9 twist 75gr custom round, 20" Stock rifle with a upgraded trigger
7B9NkQldeu0

phish
10-09-2011, 8:08 AM
repeat in December, then get back to us

videos like these are akin to spamming Lowlight's video when the subject of barrel length comes up

'Ike'
10-25-2011, 10:16 PM
Here's some great info on barrel twist and such...

http://www.ar15.com/forums/t_3_16/496347_.html

phish
10-26-2011, 1:13 AM
to quote JT:

"It is a well documented fact that if you run 77 gr. bullets in a 9 twist barrel, the universe will cease to exist."

a tome of knowledge and expertise...

Knife Edge
10-26-2011, 5:33 AM
69gr 1:9 twist 1000 yards, Savage 11 in .223 Rem. 20" barrel
CCJxQqkgGf0

DPMS AR15, 1:9 twist 75gr custom round, 20" Stock rifle with a upgraded trigger
7B9NkQldeu0

I'm gradually coming over to the line of thinking the least amount of rotational velocity necessary is the best, assuming it stays stable. 1:9 not a bad option at all..

I wish I had access to a 14.5" 1:9, I'd like to see how 69g runs out of that.