270 Win, 140 AB & RL26 Load Tweak Help

[EOD Diver]

Howdy Fellas,

Just made it back from the range after shooting my 270win. I saw where someone did a QL projection for the 140AB and it showed 62 grains of RL26 as the max load with a pressure of 64K. It was supposed to be good for about 3120 FPS out of a 22” pipe. Today at the range, my ladder went as high as 62.5, but I only made it to 3126 FPS using RL26, 140AB, Nosler unfired case, and a CCI 250 out of my 24” barrel. Any thoughts on this on how to tweak the prediction for an accurate pressure/velocity?
V/R,
Joe

 

[DrMike]

Your measured velocity is within the confidence level of projection at SAAMI standards. 62.5 grains of RL26 will only yield a projected velocity of 3151 fps. 62.0 grains projects at 3123 fps. The differential isn't all that great.

Cartridge          : .270 Win. (SAAMI)
Bullet             : .277, 140, Nosler AccuBond 54765
Useable Case Capaci: 59.393 grain H2O = 3.856 cm³
Cartridge O.A.L. L6: 3.340 inch = 84.84 mm
Barrel Length      : 22.0 inch = 558.8 mm
Powder             : Alliant Reloder-26

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   95    55.80   2767    2380   43346  13152     98.1    1.255
-09.0   96    56.42   2803    2442   45025  13279     98.5    1.233
-08.0   97    57.04   2839    2505   46776  13397     98.8    1.211
-07.0   98    57.66   2874    2569   48607  13505     99.2    1.189
-06.0   99    58.28   2910    2633   50520  13604     99.4    1.168
-05.0  100    58.90   2946    2698   52521  13691     99.6    1.147
-04.0  101    59.52   2981    2763   54614  13768     99.8    1.126
-03.0  102    60.14   3017    2829   56804  13834     99.9    1.106  ! Near Maximum !
-02.0  103    60.76   3052    2896   59097  13890    100.0    1.086  ! Near Maximum !
-01.0  104    61.38   3088    2963   61501  13933    100.0    1.067  ! Near Maximum !
+00.0  105    62.00   3123    3031   64020  13971    100.0    1.047  ! Near Maximum !
+01.0  106    62.62   3158    3099   66660  14008    100.0    1.028  !DANGEROUS LOAD-DO NOT USE!
+02.0  107    63.24   3192    3168   69432  14043    100.0    1.010  !DANGEROUS LOAD-DO NOT USE!
+03.0  109    63.86   3227    3237   72345  14077    100.0    0.992  !DANGEROUS LOAD-DO NOT USE!
+04.0  110    64.48   3262    3307   75402  14109    100.0    0.974  !DANGEROUS LOAD-DO NOT USE!
+05.0  111    65.10   3296    3378   78619  14139    100.0    0.956  !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    105    62.00   3272    3329   81474  13326    100.0    0.954  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba    105    62.00   2893    2601   49536  14186     96.5    1.170



Cartridge          : .270 Win. (SAAMI)
Bullet             : .277, 140, Nosler AccuBond 54765
Useable Case Capaci: 59.393 grain H2O = 3.856 cm³
Cartridge O.A.L. L6: 3.340 inch = 84.84 mm
Barrel Length      : 22.0 inch = 558.8 mm
Powder             : Alliant Reloder-26

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   96    56.25   2793    2425   44556  13245     98.4    1.239
-09.0   97    56.88   2829    2488   46303  13367     98.8    1.217
-08.0   98    57.50   2865    2552   48127  13478     99.1    1.194
-07.0   99    58.13   2901    2617   50033  13580     99.4    1.173
-06.0  100    58.75   2937    2682   52028  13671     99.6    1.152
-05.0  101    59.38   2973    2748   54115  13751     99.8    1.131
-04.0  102    60.00   3009    2814   56300  13821     99.9    1.110  ! Near Maximum !
-03.0  103    60.63   3045    2882   58589  13878    100.0    1.090  ! Near Maximum !
-02.0  104    61.25   3080    2949   60987  13925    100.0    1.071  ! Near Maximum !
-01.0  105    61.88   3116    3018   63502  13964    100.0    1.051  ! Near Maximum !
+00.0  106    62.50   3151    3086   66139  14001    100.0    1.032  !DANGEROUS LOAD-DO NOT USE!
+01.0  107    63.13   3186    3155   68910  14037    100.0    1.013  !DANGEROUS LOAD-DO NOT USE!
+02.0  108    63.75   3221    3225   71817  14071    100.0    0.995  !DANGEROUS LOAD-DO NOT USE!
+03.0  109    64.38   3256    3295   74874  14103    100.0    0.977  !DANGEROUS LOAD-DO NOT USE!
+04.0  110    65.00   3291    3366   78088  14134    100.0    0.959  !DANGEROUS LOAD-DO NOT USE!
+05.0  112    65.63   3325    3438   81471  14163    100.0    0.942  !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    106    62.50   3298    3381   84150  13361    100.0    0.941  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba    106    62.50   2923    2657   51101  14301     96.9    1.153

Factors that will have an impact on velocity include lot-to-lot variation, ambient temperature, jump to the lands, etc. Any of these can affect velocity. I can't see that you're being cheated with statistical variation factored in. If you don't see any signs of pressure, you can continue to increase the charge until you reach a higher velocity if required. If it was my work, I'd probably be content if accuracy was present.

 

[EOD Diver]

Doc,
Thank you! I just wanted to make sure I was reading it right. If the old rule of thumb of one inch of barrel is worth 30 FPS, does it stand to reason that my pressure is under 61K at my velocity of 3126 with the 24” pipe?
V/R,
Joe

 

[RiverRider]

I'd guess you're at 62k.

 

[RiverRider]

Oops. Missed the barrel length comment.

 

[SJB358]

Joe, I would think you’re very safe at 3100 with the 140 and 26. I’m running the 150 ABLR at 3030 from a 22.5” barrel with 26 and it’s amazingly accurate. Hope you get the results you’re looking for. I’m running the 130 Tipped TBBC with RL26 for 3150 and it seems to shoot real well. Man I do love those P64’s.

 

[EOD Diver]

Scotty,
Thanks for the sanity check. I was thinking I could make it to 3160 FPS if necessary, but am just fine below that. It’s just nice to know I’ve got a little room should it not settle in when I shoot it for groups and start to tinker with seating depth.
V/R,
Joe