The best source of info and procedure is going to be the Lee Reloading manual. It has wonderful info on down loading such as computing approx. velocities and powder charges, powder selecton, ect. For base data just use the .300 WinMag. as it is very close to case capacity of .300WSM.
The problem is not so much with KB's from the unrepeatable phenomon of "detonation", but from double charges with small charges of fast burning powders.
BTDT !!!
Last August, I was loading some plinking/practicing loads for My Interarms MkX in '06, with some 175 FNGC bullets. The 12.0gr load of Universal got doubled in one.
Locked the gun up tight !!!!!
Only damage was to small projection off of bolt face next to extractor cut. It sheared off while bolt was being hammered open. A local auto speed shop magnafluxed the action for me... it checked out with a no-go headspace gauge too. Whenever CharlesDaly starts importing the Zastava guns and parts, I'm going to get me an new bolt and intall a .338/06 bbl I have.
When loading the reduced loads, double check for powder level. More than one gun has been KB'd with double charges of pistol powders.
If you're looking to load down to 7.62x39 levels, the old standby powder for reduced "intermediate" loads is H4895 (also the IMR). If your' looking to load Cast Bullet Loads, the Lyman Cast Bullet manual is a wonderful reference. Just use the .300WinMag data, and consider maximums to be 5% under WinMag loads till you work up to them. Most maximums are not due to pressure but practical upper limits for cast bullet velocities. Most of the same weight bullets can be substituted with jacketed, but be sure to observe the 5% caveat I just mentioned.
Good Luck !!!!
BTW I've not gotten any benefit from fillers (w/.22Hornet- thru .45/70). If I were to try them again, I'd go with Puff-lon for a try.
If you can cast, the Lee .311" 155 Pt. gas check bullet over 5-8gr of Unique will probably be your best bet. Not the heavy bullet you're looking for, but will stabilize at the speeds your talking about (900-1,000 fps). You could just use bullets "as cast",and lube w/Lee Tumble lube for an accurate and very inexpensive load. I've done this w/'06 and this bullet and a .311 RN 78gr bullet. The 78gr'r w/5.0 bullseye would print to my lower taper of the crosshairs of my 2.5-8x Leupold for a wonderful plinking load. Would shoot ragged hole groups under 1" @25yds too.