As far as the 314299 casting at 314, it is supposed to with #2 alloy. But, recent reports no Lyman molds suggest you may get anywhere form .312 to .315. While larger would be good, there have been a bunch of reports of undersized molds lately. You would just have to get one and try. If it is undersized, you would have to send it back to Lyman.
Which Lee mold do you have that is supposed to cast at .314? The mold they list for the 303 Brit is listed at .312. I have had 2, one cast at .312, the other cast at .314. I still have the one that casts at .314, and it works fine in my gun. Not as well as the 314299, but decent. You say the body is at .305, where is that measured? If it is on the bands, it is seriously undersized and needs to go back to Lee. At .007 under, I'm not sure how it would stay seated in the case. It would drop right through the neck on my cases. Billy