How tight twist need 140gr 6,5mm bullets by subsonic velocity? And who makes those barrel?

Idea is changce Tikka T3 204ruger rifle new 6,5mm barrel. Original case will be 222rem neck up for 6,5mm bullets. Idea is get so accuracy subsonic rifle what is possible for 140gr bullets.

Look up JBM - Calculations, Bullet Drag and Twist. Here's an example but I did not have the bullet data so it was just a guess. (The columns lose there spacing when copied into ACR). Then you could look up 6.5 Wisper. The same twist should apply.

Calculated Table
Mach Muzz Vel CD CD CD CD CD CD BC Form Twist Stability
Number (ft/s) Nose Boattail Base Band Skin Total (G1) Factor (in) (>1.5)
0.500 558.2 0.000 0.000 0.163 0.000 0.062 0.225 0.276 1.108 11.2 1.9
0.600 669.9 0.000 0.000 0.167 0.000 0.059 0.226 0.275 1.111 11.2 1.9
0.700 781.5 0.000 0.000 0.171 0.000 0.056 0.228 0.290 1.052 11.2 1.9
0.800 893.2 0.000 0.000 0.176 0.000 0.054 0.230 0.338 0.903 11.1 1.8
0.850 949.0 0.007 0.000 0.178 0.000 0.053 0.238 0.373 0.819 11.0 1.8
0.900 1004.8 0.073 0.000 0.180 0.000 0.052 0.305 0.342 0.894 10.9 1.8
0.925 1032.7 0.102 0.000 0.181 0.000 0.052 0.335 0.340 0.897 10.8 1.7
0.950 1060.6 0.129 0.000 0.182 0.000 0.051 0.363 0.344 0.888 10.7 1.7
0.975 1088.5 0.154 0.000 0.183 0.000 0.051 0.388 0.350 0.872 10.4 1.6
1.000 1116.4 0.177 0.000 0.224 0.000 0.050 0.452 0.325 0.940 12.1 2.2
1.100 1228.1 0.370 0.000 0.221 0.000 0.049 0.639 0.281 1.086 11.2 1.9
1.200 1339.7 0.365 0.000 0.216 0.000 0.047 0.628 0.311 0.983 11.1 1.8
1.300 1451.4 0.350 0.000 0.212 0.000 0.046 0.608 0.331 0.923 11.1 1.8
1.400 1563.0 0.340 0.000 0.207 0.000 0.044 0.592 0.342 0.893 11.1 1.9
1.500 1674.7 0.332 0.000 0.202 0.000 0.043 0.577 0.348 0.878 11.2 1.9
1.600 1786.3 0.326 0.000 0.196 0.000 0.042 0.564 0.351 0.871 11.2 1.9
1.700 1898.0 0.320 0.000 0.190 0.000 0.041 0.551 0.352 0.868 11.2 1.9
1.800 2009.6 0.315 0.000 0.184 0.000 0.040 0.539 0.352 0.868 11.3 1.9
2.000 2232.9 0.307 0.000 0.171 0.000 0.038 0.516 0.351 0.870 11.3 1.9
2.200 2456.2 0.301 0.000 0.159 0.000 0.036 0.495 0.351 0.871 11.4 1.9
2.500 2791.1 0.292 0.000 0.140 0.000 0.034 0.466 0.353 0.864 11.4 2.0
3.000 3349.3 0.281 0.000 0.113 0.000 0.030 0.425 0.369 0.828 11.5 2.0
3.500 3907.6 0.273 0.000 0.091 0.000 0.028 0.392 0.393 0.778 11.5 2.0
4.000 4465.8 0.266 0.000 0.074 0.000 0.025 0.366 0.418 0.731 11.6 2.0
4.500 5024.0 0.260 0.000 0.061 0.000 0.023 0.345 0.442 0.691 11.6 2.0

Error? 17/07/09 12:04, JBM/jbmdrag