I have been messing around with QL and Applied Ballistics for weeks now concerning the 280 Ackley, I have a Nosler M48 Custom ordered in that caliber...
So far...the load below is the best I can come up with for trajectory...I have 4 lbs. of MRP powder, just need Nosler to make some 150 grain ABLR's.
Cartridge : .280 Ack Imp
Bullet : .284, 150, Nosler Accubond LR 58734 G7
Useable Case Capaci: 65.523 grain H2O = 4.254 cm³
Cartridge O.A.L. L6: 3.330 inch = 84.58 mm
Barrel Length : 24.0 inch = 609.6 mm
Powder : Norma MRP
Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.769% 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
-07.7 95 60.00 2884 2770 47834 12249 98.1 1.279
-06.9 96 60.50 2910 2820 49171 12335 98.4 1.263
-06.2 97 61.00 2935 2870 50547 12418 98.6 1.247
-05.4 98 61.50 2961 2920 51966 12497 98.9 1.231
-04.6 98 62.00 2986 2971 53428 12571 99.1 1.216
-03.8 99 62.50 3012 3022 54939 12642 99.3 1.201
-03.1 100 63.00 3038 3073 56495 12708 99.4 1.185 ! Near Maximum !
-02.3 101 63.50 3063 3125 58100 12770 99.6 1.171 ! Near Maximum !
-01.5 102 64.00 3088 3177 59757 12828 99.7 1.156 ! Near Maximum !
-00.8 102 64.50 3114 3229 61468 12881 99.8 1.141 ! Near Maximum !
+00.0 103 65.00 3139 3282 63230 12930 99.9 1.127 ! Near Maximum !
+00.8 104 65.50 3164 3335 65041 12975 99.9 1.113 !DANGEROUS LOAD-DO NOT USE!
+01.5 105 66.00 3190 3388 66904 13014 100.0 1.099 !DANGEROUS LOAD-DO NOT USE!
+02.3 106 66.50 3215 3442 68823 13049 100.0 1.085 !DANGEROUS LOAD-DO NOT USE!
+03.1 106 67.00 3240 3496 70801 13080 100.0 1.072 !DANGEROUS LOAD-DO NOT USE!
+03.8 107 67.50 3265 3550 72840 13110 100.0 1.059 !DANGEROUS LOAD-DO NOT USE!
Results caused by ± 5% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 5% relative to nominal value:
+Ba 103 65.00 3218 3448 70558 12646 100.0 1.078 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 5% relative to nominal value:
-Ba 103 65.00 3043 3085 56181 13034 98.5 1.183 ! Near Maximum !
Now I love the dear old 270 as much as anybody...but it can't quite compete with this...and this is using the Litz verified BC of the 150 grain ABLR (.295 G7)
140 grain Accubond...again, with a corrected BC.
If thats not solidly into 7mm Rem Mag territory...I'll drink the Rio Grande...the 280 Ackley is essentially a "long" 7mm Remington Short Action Ultra mag...the case capacities are very nearly idectical....and the standard 270 Win isn't even close (~100 fps behind)...now, if you Ackley the 270....things even out a bit.
A lot of folks mention Hodgden's online load data for the 280 Ackley...it appears Hodgden didn't load the 280 Ackley much past 60,000 psi for their testing...leaving 5,000 psi on the table, hence the lower velocities they show...I think they rushed to get data available (a good thing) and didn't quite do all their homework on the pressure limit as set by SAAMI.
One more thing...about the pressure limit of the 7mm Rem Mag...SAAMI set it at 61,000 psi because the 7mm RM is very prone to random pressure spikes which can send it well into unsafe territory if its loaded any hotter with certain load combinations...other rounds suffer this too, the 243 Win for example.
Very few rounds are SAAMI spec'd at 65,000 psi...and of those few...most, but not all, are relatively new rounds using modern case designs.
http://www.saami.org/specifications_and_information/specifications/Velocity_Pressure_CfR.pdf
Just a few things I felt were worth throwing in here...