Lee and Alliant Loading Data
I see that you are looking at the data provided in the Lee 308 Win Die set. It does state that the maximum RL-15 load, for a minimum COAL of 2.700”, is 49.0 grains. Note that it does not specify the manufacturer and/or the style of bullet. Velocity is reported as 2919 fps.
I checked the Alliant Reloader’s Guide for 308 Win data. Alliant provides data on a Speer 150 grain SP bullet. Alliant states that the “not to exceed” load is also 49.0 grains of RL-15. The minimum COAL is also 2.700”. Reported velocity is 2919 fps. Lee may be using the Alliant data.
Both QuickLoad and GRT software programs have data for a Speer 150 grain SP (2023) bullet as well as Alliant RL-15 powder. I ran both programs to see how the QL and GRT results compare with the Lee and Alliant data. Lee does not state a barrel length but Alliant provides a barrel length of 22”. Care was taken to ensure that all the programs input parameters such as COAL, bullet length, temperature, effective case capacity and barrel length were the same. I also wanted to compare one program’s results against the other program’s results. Below is a comparison of results.
Speer 150 grain SP (2023)
Load Data---------------------Lee---------Alliant-------------QL------------------GRT
Velocity------------------------2919--------2919-------------2942----------------2910
Chamber Pressure------------????---------????--------------62,504--------------63,976
Load Ratio -------------------????---------????--------------105.7%-------------103.8%
The calculated velocities from the two models are very close to the measured velocity from Alliant. The North American SAAMI maximum pressure for the 308 Win is 62,000 psi. Both models predict pressures above the SAAMI maximum pressure.
I understand you will be using some FMJ bullets in your loads and will be starting at a much-reduced powder charge. This is wise since you will be using a bullet that is different from the bullet used in the Alliant data. Using the FMJs and the maximum given load could be problematic. I suspect the FMJs are longer than the Speer SPs used in the reload data. As an example, the Speer SP is 1.032” long. The Speer BT FMJ is 1.173” long. If the FMJs were loaded to the same COAL as the SPs, effective case capacity would be reduced, and chamber pressure will be increased. Seating the FMJ bullet 0.141” deeper in the case predicts chamber pressures well above the SAAMI maximum pressure.
Speer 150 grain BT FMJ (2018)
Load Data------------------------QL------------------GRT
Velocity-------------------------3001----------------2973
Chamber Pressure-------------68,610--------------70,699
Load Ratio --------------------110.0%-------------108.0%
Many members on this Site have stressed that you should always start low, when developing a load, and work up while looking for indications of pressure issues. This is great advice as can be seen in this example.
Have fun with your new rifle.