Re: 243 short barrel powder choice
Try IMR 4064. It works well with light and heavy bullets. If your rifle has a twist rate of 1 in 10, then I would stay away from 100 grain bullets. 1 in 10 is not fast enough to give good stability to a 100 gr bullet. If your twist rate is 1 in 9 or faster, then stability is not an issue. 90gr bullets and lighter work well in a barrel with either 1 in 9 or 1 in 10 twist rates.
Check your manual for the proper charges, but I think you will be pleased with the performance of IMR 4064 with any bullet weight you choose to load. (As long as your rate of twist is matched correctly with your bullet of choice.)