I suspect that OAL is limited by the magazine box not the throat. I load many calibers in the compressed persuasion, if fact I prefer it. I have found that I generally achieve best performance with the slowest powder that will achieve the desired pressure/velocity. Is your current load within the Barnes Reloading Manual maximum? Also, note that you can use lighter than typical weights when using the X or TSX bullets. I always drop down a notch or two from typical. The 150 gr is plenty and I have used the 130 gr X in the 308 with good success.