MY dad shoots the 139 GMX in his .280 Rem. He loves them and mentioned it when through both shoulders and retained 95 or 98% of its weight. I would imagine the .257 cal GMX will perform the same in regards to weight retention.
For your powder choice and load, whats your barrel length? Using 24", 66gr H2O capacity, 3.200 OAL, You can expect a good node around ~47 gr. There is another OBT node at 51gr, but definitely work up as it is close to dangerous pressures. Really depends on barrel length, case capacity, oal, and chronographed velocity.
Cartridge : .25-06 Rem.
Bullet : .257, 90, Hornady GMX 22410
Useable Case Capaci: 59.375 grain H2O = 3.855 cm³
Cartridge O.A.L. L6: 3.200 inch = 81.28 mm
Barrel Length : 24.0 inch = 609.6 mm
Powder : Accurate 4350
Predicted data by increasing and decreasing the given charge,
incremented in steps of 1.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !
Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms
-10.0 82 45.00 3007 1807 45695 10241 97.2 1.151
-09.0 83 45.50 3038 1845 46865 10340 97.6 1.139
-08.0 84 46.00 3069 1882 48074 10435 97.9 1.128
-07.0 85 46.50 3100 1920 49324 10527 98.2 1.117
-06.0 86 47.00 3130 1958 50615 10616 98.4 1.106
-05.0 87 47.50 3161 1997 51948 10702 98.7 1.095
-04.0 88 48.00 3191 2036 53326 10783 98.9 1.084
-03.0 89 48.50 3222 2075 54749 10861 99.1 1.073
-02.0 90 49.00 3252 2114 56218 10935 99.3 1.062 ! Near Maximum !
-01.0 90 49.50 3283 2153 57735 11005 99.5 1.051 ! Near Maximum !
+00.0 91 50.00 3313 2193 59302 11071 99.6 1.041 ! Near Maximum !
+01.0 92 50.50 3343 2233 60920 11132 99.7 1.030 ! Near Maximum !
+02.0 93 51.00 3373 2274 62592 11189 99.8 1.020 ! Near Maximum !
+03.0 94 51.50 3403 2314 64318 11242 99.9 1.010 ! Near Maximum !
+04.0 95 52.00 3433 2355 66102 11290 100.0 1.000 !DANGEROUS LOAD-DO NOT USE!
+05.0 96 52.50 3463 2396 67944 11334 100.0 0.989 !DANGEROUS LOAD-DO NOT USE!
Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba 91 50.00 3456 2386 69324 10682 100.0 0.986 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba 91 50.00 3116 1940 49702 10962 95.3 1.110
These powders and estimated charges are alternatives:
Powder type Filling/Loading Ratio Charge Charge Vel. Prop.Burnt P max P muzz B_Time
% Grains Gramm fps % psi psi ms
Alliant Reloder-33 103.8 62.4 4.05 3173 86.1 49085 12083 1.106
Norma MRP 90.6 51.8 3.35 3145 94.7 46747 11489 1.106
Alliant Reloder-25 97.3 53.0 3.43 3144 96.9 45963 11333 1.106
Alliant Reloder-17 80.5 46.2 3.00 3142 99.3 46668 10693 1.106
Hodgdon Retumbo 104.0 57.3 3.71 3140 94.7 45815 11685 1.106
Accurate 4350 85.8 47.0 3.04 3129 98.4 50575 10614 1.106
Accurate 4064 80.8 43.3 2.81 3128 100.0 53301 9492 1.106
Vihtavuori N170 108.5 58.8 3.81 3123 86.3 54137 10824 1.106
Vihtavuori N550 83.5 46.7 3.03 3123 98.1 49749 10614 1.106
