You will be fine to use magnum primers, just work up a load as per normal safe methods. Im using BR2s in my 243AI. Your going to use primers at whatever pace you use them at and will eventually need to buy more so why not just go to a LR primer for the 243 and be done with it. Its not to say that you can't use em, Id just say you may find very little info for 2213SC and a magnum primer. Id also suggest a crony will show you what is really happening. You may get really crap ES or other undesirable but it is just the same with a LR primer.
Bookmarks