Ted,
78 grains would be a very bad idea. So would 75. I don't think you could get 78 grains in the case with that 225gr bullet.
I don't know who you've been listening to, or what they were smoking, but it's time to stop paying attention to anything they have to say:
Cartridge : .338 Win Mag.
Bullet : .338, 225, Barnes 'TTSX' S 30430
Useable Case Capaci: 69.939 grain H2O = 4.541 cm³
Cartridge O.A.L. L6: 3.340 inch = 84.84 mm
Barrel Length : 26.0 inch = 660.4 mm
Powder : Alliant Reloder-19 *C
Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.714% 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
-07.1 101 65.00 2638 3476 47209 8370 95.2 1.369
-06.4 102 65.50 2658 3531 48363 8435 95.5 1.354
-05.7 102 66.00 2679 3586 49546 8498 95.8 1.339
-05.0 103 66.50 2700 3642 50762 8559 96.1 1.325
-04.3 104 67.00 2721 3698 52010 8619 96.4 1.311
-03.6 105 67.50 2741 3754 53294 8677 96.7 1.296 ! Near Maximum !
-02.9 105 68.00 2762 3811 54611 8734 96.9 1.283 ! Near Maximum !
-02.1 106 68.50 2783 3869 55963 8789 97.2 1.269 ! Near Maximum !
-01.4 107 69.00 2803 3927 57355 8843 97.4 1.255 ! Near Maximum !
-00.7 108 69.50 2824 3985 58785 8895 97.7 1.242 ! Near Maximum !
+00.0 109 70.00 2845 4044 60254 8945 97.9 1.228 ! Near Maximum !
+00.7 109 70.50 2866 4103 61766 8993 98.1 1.216 !DANGEROUS LOAD-DO NOT USE!
+01.4 110 71.00 2886 4162 63320 9039 98.3 1.203 !DANGEROUS LOAD-DO NOT USE!
+02.1 111 71.50 2907 4222 64920 9084 98.5 1.190 !DANGEROUS LOAD-DO NOT USE!
+02.9 112 72.00 2928 4283 66565 9126 98.7 1.177 !DANGEROUS LOAD-DO NOT USE!
+03.6 112 72.50 2949 4344 68260 9167 98.9 1.165 !DANGEROUS LOAD-DO NOT USE!
Results caused by ± 3% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 3% relative to nominal value:
+Ba 109 70.00 2890 4172 63853 8937 99.0 1.200 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 3% relative to nominal value:
-Ba 109 70.00 2796 3906 56789 8910 96.5 1.260 ! Near Maximum !