Hi,
This is my first post on this forum, I have 10 years reloading experience but none with subsonics. I have been playing around with quickload software to see what is possible, I have no intention to go this low with my powder charge but I am attempting to understand the principals. Once you go below a certain charge you seem to get a “Shot start pressure for this data too high” message. This is an odd message to get because maximum pressure and start pressure should drop as the charge drops (unless I am mistaken). Here is the data I am entering and the output data -
Cartridge: 308 Winchester
For reference I have selected COAL 2.81”
Barnes 180gr boat tail projectile
Powder Fill % Start Pressure Max chamber pressure M.V.
14gr 99.9 4351 PSI 33372 PSI 1475 fps
13gr 92.8 4351 30080 1419
12gr 85.7 4351 26922 1360
11gr 78.6 4351 23890 1299
10gr 71.4 4351 20978 1236
9gr 64.2 4351 18176 1168
8gr 57.1 4351 15469 1097
7gr 50 4351 12801 1019
6gr 42.9 Shot start pressure for this data too high, max 4075
5gr 35.7 Shot start pressure for this data too high, max 3341
This data proves that the start pressure does eventually drop slightly. However I basically don’t understand what is going on here; I don’t understand how start pressure can be constant from 14 to 7 grains then suddenly the “maximum start pressure” starts dropping, it drops to 4075 PSI, which is lower than 4351 PSI, but it is still too high all of a sudden? I thought maximum start pressure should be the same no matter how much powder is in the case?
Matt.
