John,
I use to have a Bullberry 15inch in this caliber. It was so accurate I would shoot about a hundred rounds through it a setting and not let it cool. I ended up degrading the accuracy and had it rebored to 7mm and chamber for the Waters round.
It is the most accurate barrel I have ever owned and wish I was smart enough to take better care of it. Numerous 5 shot groups at 100 yards you could cover with a quarter.
Unfortunately I didn't keep the best records back then and don't have the exact load. I do remember the following though. I only used the 75gr hp by Hornady and Sierra. They grouped identical in this gun.
Best load was right around 23grs of H322 and I remember it didn't vary much with a grain more or less. I would start around 22grs. I also remember using H335, AA2230, and AA2460 with no real change in groups with these bullets. H335 just has more flash and blast. It was a very easy cartridge to load for but I seem to remember H322 gave me the best velocity for pressure. I also remember starting loads for the 223 with a 50gr bullet out of the Sierra 3rd edition manual were a great starting point as they never got me in trouble. I can't verify any other manuals as that was the only one I used at the time.
Hope this gets you started.
Scott.
