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Twist Tables

Use the information on the Twist Rate & Stability Tables below to help pick the right bullet …

The following tables are based on the Greenhill Formula. Using them will allow you to estimate the heaviest/longest bullet a gun will stabilize based on the caliber (left-most column) and twist rate in inches (top-most row). For example, a 45 (.457) caliber rifle with a twist rate of 1 in 18″, should be able to stabilize a bullet up to 672 grains or 1.74″ in length.

Maximum Weight of Bullet Stabilized (grains)

Twist>>78910111213141516171819202122
Caliber
0.429939854783723671626587553552494470447427
0.457931864806756712672637605576550

Maximum Length of Bullet Stabilized (inches)

Twist>>78910111213141516171819202122
Caliber
0.4293.943.453.072.762.512.302.121.971.841.731.621.531.451.381.311.25
0.4574.483.923.483.132.852.612.412.242.091.961.841.741.651.571.491.42

The Greenhill Formula does not, however, take into account bullet shape or muzzle velocity. Both parameters come into play especially when you approach the limit of what a caliber/twist rate combination should stabilize.

Consider a bullet as a cylinder. A round-nosed bullet is more like a cylinder, has its weight very evenly distributed along its entire length and takes less spin to stabilize. On the other hand, a spitzer-shaped bullet has most of its weight contained within the base half of the bullet. The center of mass is therefore not the middle of the bullet and it will require more spin to keep the nose and base aligned. The moral of the story? When you approach theorized limit of what a caliber/twist rate combination should stabilize, stay away from spitzer-shaped bullets. That is, unless you can keep velocity high.

Every shooter knows the term velocity. The reloading manuals are full of ballistic tables showing velocity at the muzzle and 100, 200, 300, etc. yards down range. I’ll bet, however, that most shooters don’t realize that velocity and twist rate determine the speed at which a bullet spins. That spin rate, in revolutions per second or minute, keeps the base and nose of the bullet traveling in the same direction. For example, let’s consider the same 45 caliber rifle with a 1 in 18″ twist rate. At a muzzle velocity of 1,000 feet per second (fps), the bullet is spinning at 666.67 revolutions per second (rps) or 40,000 revolutions per minute (rpm). At a muzzle velocity of 2,000 fps, that same bullet will be spinning at 1333.3 rps or 80,000 rpm. By contrast, take a 22-250 varmint rifle with a 1 in 12″ twist firing a bullet at 3,600 fps. That bullet is spinning at 3,600 rps of 216,000 rpm. The moral of the story? When you approach the theoretical limit of what a caliber/twist rate combination should stabilize and your bullets are keyholing on the target, increase the muzzle velocity (if you can and still stay safe), switch to a more round-nosed bullet shape, or switch to a slightly lighter/shorter bullet.

Use these tables as a general guideline only. I tell all of my long-range shooting customers, shoot the longest, heaviest bullet that your rifle shoots best. Accuracy is more important in the long-range game than muzzle velocity or bullet shape. And yes, Virginia, you must experiment with many different bullets in order to find the one your rifle likes. And that’s why we have the selection we do!

Maximum Weight of Bullet Stabilized (grains)

Twist>>78910111213141516171819202122
Caliber
0.224100877870635854504744413937353332
0.24414012310998898276706661585552494745
0.25717315113412111010493868176716764605855
0.264192168150135122112104969084797571676461
0.277233204181163148136126117109102969186827874
0.28425822620018016415013912912011310610095908682
0.308357312277250227208192178166156147139131125119113
0.311371324288259236216200185173162153144137130124118
0.323431377335302274252232216201189178168159151144137
0.338517452402362329302278259241226213201191181172165
0.348581508452407370339313291271254239226214203194185
0.357644563501451410375347322300282265250237225215205
0.375784686609548499457422392366343323305289274261249
0.410980871784712653603560522490461435412392373356
0.429939854783723671626587553522494470447427
0.457931864806756712672637605576550

Maximum Length of Bullet Stabilized (inches)

Twist>>78910111213141516171819202122
Caliber
0.2241.080.940.840.750.680.630.580.540.500.470.440.420.400.380.360.34
0.2441.281.120.990.890.810.740.690.640.600.560.530.500.470.450.430.41
0.2571.421.241.100.990.900.830.760.710.660.620.550.620.580.500.470.45
0.2641.491.311.161.050.950.870.800.750.700.650.610.580.550.520.500.48
0.2771.641.441.281.151.050.960.890.820.770.720.680.640.610.580.550.52
0.2841.731.511.341.211.101.010.930.860.810.760.710.670.640.600.580.55
0.3082.031.781.581.421.291.191.091.020.950.890.840.790.750.710.680.65
0.3112.071.811.611.451.321.211.121.040.970.910.850.810.760.730.690.66
0.3232.241.961.741.561.421.301.201.121.040.980.920.870.820.780.750.71
0.3382.452.141.901.711.561.431.321.221.141.071.010.950.900.860.820.78
0.3482.602.272.021.821.651.511.401.301.211.141.071.010.960.910.870.83
0.3572.732.392.121.911.741.591.471.371.271.191.121.061.010.960.910.87
0.3753.012.642.342.111.921.761.621.511.411.321.241.171.111.051.000.96
0.4103.603.152.802.522.292.101.941.801.681.581.481.401.331.261.201.15
0.4293.943.453.072.762.512.302.121.971.841.731.621.531.451.381.311.25
0.4574.483.923.483.132.852.612.412.242.091.961.841.741.651.571.491.42

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