Can anyone tell me if the speer .451 jsp 300 grn is good to reload for 45 acp. I can't find any info about it online or in my Accurate reloading manual. Any help is appreciated.

I don't think you could even get one into a case & make it function through a magazine, so my question would be, why?

Rick-
In short, the answer is no. I played around with the 250 grain bullets some years back with less than good results. Not only did the 250s not feed in my 1911, the only (somewhat) usefull powder is Unique.

It isn't the diameter I am worried about. It is the length. The added pressure could cause potential problem. I have made a couple of these bullets and they fit into the case. They are just seated a little more deeply than other bullets. The overall case lenth is still well within regs.