Who said manuals are Gospel?
CB - I think I found that load you cited. Page 44 of "The Complete Reloading Manual for the 356 & 358 Winchester" has that load listed by Barnes Bullets. This is in the 358Win section. Several other pages in the same manual show loads surpassing 2300fps with a 250gr bullet. Also states a 26inch barrel, or some other variant like a pressure barrel, etc, all of which give a distorted view of what is happening upon exit.
Manuals are but a guide, but should have some modicum common data. If there is a lot of disparity between the manuals, than we have to look at the test equipment and components to sort the variables to where we can pass judgment on the written page. When you get ready to load the cases for your 250gr bullets, be kind to your rifle. Let it have a say in the matter. It will tell you if it appreciates what you are trying to accomplish, or not. All 250gr bullets wii not reach the same velocity with the same powder charge. What's a guy to do?!? Take the rifle, load it, and shoot it....and listen...it will tell you if more is better, or not. The longer your barrel, the more likely you are to reach this goal. If it's a carbine, don't ruin it by trying to make it do something it was never intended to do; keep a lid on the pressures. I don't know of any animal that needs a 250gr 35Cal bullet at 2300fps to put it down.
My 356Win will top 2200 with factory 250's, my handloads are in the same neighorhood. I sort of wish for a 225gr flatnose, but guess that will have to come from LBT!
Regards,
Sweetwater