Selecting a Twist Rate for Your AR

Short Story: The ideal twist rate depends several attributes of the projectile. Pick the tab for your cartridge, below, for your short answer.

If you are here, you want to know what twist rate to use for your gun.  So, we’ll get down to it.

In this article, we are delivering the punchline. If you want to hear the joke, check out the Para Bellum University articles on Ballistics.

The ideal twist rate is dependent on the bullet and cartridge. Many sites out there make blanket statements like, “for 62 grain bullets you want 1 in 7 inches” or “1 in 7 inches is good 60-80 grain bullets”; you cannot separate the bullet from the cartridge for this discussion.  As you will see, the ideal twist rate for bullets of the same weight can be different, depending on the ballistic coefficient and length of the bullet and on the muzzle velocity of the cartridge out of a given barrel length.

If you are willing to take our word for it, the tables below have been populated based on values from either the Applied Ballistics or Strelok Pro bullet databases (Tables 1; as indicated) and calculation of gyroscopic stability factor using the Berger Twist Rate Stability Calculator for commercially available factory ammunition (Tables 2).  If you’re not willing to take our word for it (or if you want to double check our calculations), we encourage you to go do the calculation yourself; if you are using the same numbers and the same calculator, you’ll get the same result.

Introduction to Gyroscopic Stability Factor

The numbers in Tables 2 are the gyroscopic stability factor, Sg. This is a ratio of stabilizing forces and destabilizing forces. Put simply, a gyroscopic stability factor of 1.000 indicates that the destabilizing forces and the stabilizing forces are equal. If the Sg is less than 1.000, the destabilizing forces are greater than the stabilizing forces, so the bullet is not gyroscopically stable and will not perform well under any circumstances.  If the Sg is greater than 1.000, the destabilizing forces are less than the stabilizing forces, so the bullet is technically gyroscopically stable.

An Sg between 1.000 and 1.500 indicates marginal gyroscopic stability at the muzzle; it is not ideal, but the bullet might fly ok.  You want an Sg of 1.500 or higher; this will guarantee gyroscopic stability under most conditions and you will achieve the maximum ballistic coefficient.  The generally accepted “safe” Sg is 2.0, so that is what you should be targeting.  Some experts claim that excessively high Sg can lead to poor accuracy at long distances; we won’t put a number on it because there is conflicting opinion among experts, but if you are in the precision long range game, aim for an Sg around 2.0.

If you have no interest in Sg or the calculation thereof, know this: for Table 2, green is good; dark green is your best bet for the given cartridge (Sg >= 2.000).

  • 9mm

  • 223/5.56

  • 300 BLK

  • 308

  • 6.5 CM

What twist rate should I use for 9mm Luger?

Short Answer: Don’t worry about it. 9mm AR barrels come standard in 1:10″ twist and that is way more than enough to stabilize any 9mm bullet.

Any barrel with a twist rate faster than 1:29″ will stabilize a Federal 115gr FMJ 9mm bullet. The Sg for this round fired out of a short barrel with a standard 1:10″ twist is around 12.3, which is extremely high, and it will only climb with a longer barrel (due to increased velocity).

Any barrel with a twist rate faster than 1:32″ will stabilize a Federal 147gr FMJ 9mm bullet. The Sg for this round fired out of a short barrel with a standard 1:10″ twist is around 15.0, which is extremely high, and it will only climb with a longer barrel (due to increased velocity).

Suffice to say, your 9mm bullet will be in the dirt long before it loses gyroscopic stability in flight.

What twist rate should I use for .223 Remington or 5.56 NATO?

Short Answer: If you don’t want to glance down at the tables below to find the best twist rate for your cartridge, go with 1:7” twist.  As long as you’re not shooting frangible bullets, you’ll be fine.

Table 1: Bullet/Cartridge Data
Cartridge Number Bullet Bullet Weight Bullet Length* G1 B.C.* G7 B.C.* M.V.**
1 Hornady FMJ 5.56 (M193) 55 0.741 0.242 0.124 3240 (20")
2 Federal XM193 55 0.745 0.243 --- 3300
3 Federal AE FMJ 5.56 (XM193) 55 0.745 0.246 --- 3165
4 Federal XM855 62 0.907 0.304 --- 3000
5 Black Hills Sierra MK 69 0.9 0.305 --- 2875
6 Black Hills Sierra TMK 69 0.982 0.365 --- 2875
7 Berger Target BT 73 0.961 0.350 0.179 2820 (20")
8 Hornady ELD Match 73 1.049 0.410 0.210 2790 (24")
9 Hornady SP Match 75 0.981 0.395 --- 2910
10 Black Hills Sierra MK 77 0.994 --- 0.19 2750
11 Berger Tactical OTM 77 1.011 0.375 0.192 2750 (20")

* Based on the values from the manufacturer, Applied Ballistics bullet database, Strelok Pro bullet database, or JBM bullet database.

** Based on manufacturer’s specifications. If provided, the length of barrel used to collect the velocity is indicated in parentheses.

Table 2: Gyroscopic Stability for Select Cartridges
Cartridge (Table 1) Bullet Weight 1:14" 1:12" 1:10" 1:9" 1:8" 1:7"
1 55 0.999 1.36 1.96 2.42 3.06 3.99
2 55 0.990 1.35 1.94 2.39 3.03 3.96
3 55 0.976 1.33 1.91 2.36 2.99 3.90
4 62 0.615 0.838 1.21 1.49 1.88 2.46
5 69 0.691 0.940 1.35 1.67 2.11 2.76
6 69 0.537 0.730 1.05 1.30 1.64 2.15
7 73 0.601 0.817 1.18 1.45 1.84 2.40
8 73 0.464 0.631 0.909 1.12 1.42 1.86
9 75 0.587 0.799 1.15 1.42 1.80 2.35
10 77 0.570 0.775 1.12 1.38 1.74 2.28
11 77 0.542 0.738 1.06 1.31 1.66 2.17

Table 2 Assumptions:

  • Muzzle Velocity: Equal to cartridge manufacturer’s claim.
  • Ambient Temperature: 59°F
  • Altitude: 0 ft (sea level)

What twist rate should I use for .300 AAC Blackout?

Short Answer: If you don’t want to glance down at the tables below to find the best twist rate for your cartridge, go with 1:7” twist for subsonic ammo or 1:8″ twist for all other ammo. These happen to be the twist rates that you will find in most factory barrels.

Table 1: Bullet/Cartridge Data
Cartridge Number Bullet Bullet Weight Bullet Length* G1 B.C.* G7 B.C.* M.V.**
1 Winchester USA FMJ 125 1.1 0.272 --- 2185
2 Hornady AG HP 125 1.1 0.320 --- 2175
3 Federal AE FMJBT 150 1.260 0.406 --- 1900
4 Hornady SUB-X 190 1.6 0.437 --- 1050
5 Hornady A-Max 208 1.532 0.635 0.325 1020
6 Federal Suppressor OTM 220 1.6 0.650 --- 1000

* Based on the values from the manufacturer, Applied Ballistics bullet database, Strelok Pro bullet database, or JBM bullet database.

** Based on manufacturer’s specifications. If provided, the length of barrel used to collect the velocity is indicated in parentheses.

Table 2: Gyroscopic Stability for Select Cartridges
Cartridge (Table 1) Bullet Weight 1:11" 1:10" 1:9" 1:8" 1:7" 1:6"
1 125 1.89 2.28 2.82 3.57 4.66 6.34
2 125 1.88 2.28 2.81 3.56 4.65 6.33
3 150 1.46 1.77 2.18 2.76 3.61 4.92
4 190 0.759 0.918 1.13 1.43 1.87 2.55
5 208 0.934 1.13 1.40 1.77 2.31 3.14
6 220 0.864 1.05 1.29 1.63 2.13 2.90

Table 2 Assumptions:

  • Muzzle Velocity: Equal to cartridge manufacturer’s claim.
  • Ambient Temperature: 59°F
  • Altitude: 0 ft (sea level)

What twist rate should I use for .308 Winchester or 7.62 NATO?

Short Answer: If you don’t want to glance down at the tables below to find the best twist rate for your cartridge, go with 1:10” twist.  This is pretty much the standard twist rate for .308 Winchester, and you can see why by looking at Table 2. Some very heavy bullets (230 gr and 250 gr) may like faster twists, but you probably won’t be able to feed them through an AR due to the excessive cartridge length.

Table 1: Bullet/Cartridge Data
Cartridge Number Bullet Bullet Weight Bullet Length* G1 B.C.* G7 B.C.* M.V.**
1 PMC FMJBT 147 1.16 0.398 --- 2780
2 Hornady SST 150 1.153 0.365 0.187 3000
3 Hornady SST 165 1.274 0.438 0.224 2840
4 Sierra MatchKing 168 1.215 0.417 0.214 2650
5 Barnes TTSX 168 1.416 0.455 0.233 2700
6 Hornady ELD Match 168 1.279 0.511 0.261 2700
7 Hornady SP ELD Match 168 1.279 0.511 0.261 2840
8 LC M118LR OTM 175 1.240 0.474 0.243 2580
9 Sierra MatchKing 175 1.240 0.479 0.241 2600
10 Berger Tactical OTM 175 1.258 0.514 0.263 2668
11 Barnes Match Burner 175 1.335 0.517 0.265 2600
12 Hornady ELD Match 178 1.322 0.540 0.276 2600
13 Berger Tactical Juggernaut OTM 185 1.346 0.555 0.284 2608

* Based on the values from the manufacturer, Applied Ballistics bullet database, Strelok Pro bullet database, or JBM bullet database.

** Based on manufacturer’s specifications. If provided, the length of barrel used to collect the velocity is indicated in parentheses.

Table 2: Gyroscopic Stability for Select Cartridges
Cartridge (Table 1) Bullet Weight 1:12" 1:11" 1:10" 1:9" 1:8" 1:7" 1:6"
1 147 1.73 2.06 2.50 3.08 3.90 5.10 6.94
2 150 1.85 2.20 2.66 3.28 4.16 5.43 7.39
3 165 1.50 1.78 2.16 2.66 3.37 4.40 5.99
4 168 1.71 2.03 2.46 3.04 3.84 5.02 6.83
5 168 1.10 1.31 1.59 1.96 2.48 3.24 4.41
6 168 1.48 1.76 2.13 2.63 3.33 4.35 5.93
7 168 1.51 1.79 2.17 2.68 3.39 4.43 6.03
8 175 1.66 1.98 2.39 2.96 3.74 4.89 6.65
9 175 1.67 1.98 2.40 2.96 3.75 4.90 6.67
10 175 1.61 1.92 2.32 2.87 3.63 4.74 6.45
11 175 1.35 1.60 1.94 2.39 3.03 3.96 5.39
12 178 1.41 1.68 2.03 2.50 3.17 4.14 5.64
13 185 1.39 1.66 2.00 2.47 3.13 4.09 5.57

Table 2 Assumptions:

  • Muzzle Velocity: Equal to cartridge manufacturer’s claim.
  • Ambient Temperature: 59°F
  • Altitude: 0 ft (sea level)

What twist rate should I use for 6.5mm Creedmoor?

Short Answer: If you don’t want to glance down at the tables below to find the best twist rate for your cartridge, go with 1:8” twist.  This is pretty much all you will find in factory barrels. If you are having a barrel custom-made, you are probably best off with a 1:7″ twist.

Table 1: Bullet/Cartridge Data
Cartridge Number Bullet Bullet Weight Bullet Length* G1 B.C.* G7 B.C.* M.V.**
1 Federal OTM 120 1.17 0.406 --- 2900
2 Hornady ELD Match 120 1.203 0.466 0.238 2910
3 Berger Hybrid Hunter VLD (Federal) 130 1.321 0.564 0.289 2875
4 Sierra MatchKing HPBT (Federal) 140 1.303 0.529 0.271 2675
5 Hornady ELD Match 140 1.380 0.589 0.296 2710
6 Berger Hybrid Target (Federal) 140 1.402 0.608 0.306 2925
7 Hornady ELD Match 147 1.433 0.629 0.316 2695

* Based on the values from the manufacturer, Applied Ballistics bullet database, Strelok Pro bullet database, or JBM bullet database.

** Based on manufacturer’s specifications. If provided, the length of barrel used to collect the velocity is indicated in parentheses.

Table 2: Gyroscopic Stability for Select Cartridges
Cartridge (Table 1) Bullet Weight 1:10" 1:9" 1:8" 1:7"
1 120 1.51 1.86 2.36 3.08
2 120 1.39 1.72 2.18 2.84
3 130 1.14 1.41 1.79 2.33
4 140 1.25 1.55 1.96 2.55
5 140 1.06 1.31 1.66 2.17
6 140 1.04 1.29 1.63 2.12
7 147 0.997 1.23 1.56 2.04

Table 2 Assumptions:

  • Muzzle Velocity: Equal to cartridge manufacturer’s claim.
  • Ambient Temperature: 59°F
  • Altitude: 0 ft (sea level)

Don’t Stop Here!

If you are interested in learning just about everything you might need to know to understand gyroscopic stabilization, twist rate, and external ballistics, head on over to our Para Bellum University section on Ballistics!

Go To The College of Ballistics
Return to Design Considerations
Continue to Mass and Gas

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