cam69conv - Neither of the two No4 Mk1s seem to have any real preference for either .311 or the .312 Hornaday. Both bullets group equally well. Interestingly though, the .311s group about 3" higher on the target than the .312s. Every critter I have shot with the 303 with either load reacts the sme - they drop.
The most accurate off the shelf .311s - 180 gn bullets seem to be the S&B fmjs. I do not doubt that their 150 gn soft points would be of the same quality. However, that being said, there is nothing like a round nose soft point for good terminal effect.
Also however, both loads I listed are the only loads listed for those bullets with the powders mentioned and although safe in my rifles I would be hesitant about using them in someone else's rifles without working them up first.
The 303 Brits are great rifles but they are milsurps and all have significant variances. Both my No 4s have proper headspace but generous chambers and at the loading listed my brass do not last more than 3 loads. S&B brass lasts for two loads. Maybe of I just neck sized they would last longer and I will have to see if that works. But, with this in mind I am hesitant to create loads for someone else's rifles.
I usually find the factory loads by Rem or Win are usually about 100'sec slower than the S&Bs or reloads. However, if your rifle groups that well, an additional 100'/sec isn't going to matter on that whitetail and you may already have found the loads that match up to your rifle.
I know what you mean about the expenditures you have made but there is an inexpensive way to go about this - the Lee Loader is a handheld mechanism that uses standard reloading dies and is inexpensive. Also, a single stage reloading press, a used one that the previous owner felt he needed to upgrade, can be found inexpensively. You don't have to spend large amounts of $ to begin reloading and that might be something Moma will appreciate ( one can only hope).
If you want, you can pm me but I would rather talk you through the process for yourself than to hear that one of the loads has come apart in your rifle and that you have been injured. This may sound a bit parochial (? sp) but I would rather continue to read your posts than hear of an accident. Mikey.