Pardon me for starting multiple threads, but as a newbie to cast bullets I have lots of questions. Additionally with the change in the weather here, this is becoming more theory lesson for me. I will be loading during the winter for shooting in the spring.

I have a decent supply of commercial hard cast 30 cal bullets (115gr, 166gr). I haven’t found an accurate load. My jacketed load is better, but not great. There have been a whole pile of reasons why I am back to the drawing board (for both jacketed and cast and for both 30-06 and 308).

It looks like I will be blindly loading this winter and shooting in the spring. I could use some recommended starting and stopping points. I have several different powders including Red Dot and Green Dot, as well some more common powders for 308 and 30-06.

My first question to you is, what is the diameter of the two bullets in question? In theory, the bore of your .30 caliber rifles is .300 with a groove diameter of .308 although the several Marlin Microgrooves I've slugged ram .3085" for groove diameter.
So, my first suggestion is to measure those commercial bullets. While .309" is OK, my preference is for .310" for best accuracy.
The 115 gr. bullets are too short to seat so that they slightly engage the rifling but the 166 gr. bullets should be long enough. They don't have to be jammed into the rifling to the point that extracting the round leaves the bullet stuck in the throat.
Take one of the 166 gr. bullets and stick the nose of the bullet into the muzzle of the rifles in question. They should at least be a reasonably snug fit. Any looseness will mean a loss of accuracy.
The 115 gr. bullets, regardless of seating depth will have a long jump to the rifling. They're more suitable for plinking and small game if you can get an accurate load.
A load that have worked for me using 115 to 120 gr. cast bullets for gallery loads are 5.0 gr. of Unique with a 1/4 square of toilet paper to hold the small charge against the primer. Either Red or Green dot in that charge range should work OK but be very careful about getting a double charge.
I shoot a heavier bullet in both the .308 Win. and 30-06 but the charge for bullets ranging from 150 gr. to 200 gr. is the same in both cartridges. Try 16.0 gr. of Alliant #2400, 17.0 gr. of 4227 or 25.0 gr. of 4895. I use a one grain tuft of dacron seated lightly against the powder to hold it against the primer but try it both with and without the filler. My best load for the .308 Win. is 25.0 gr. of H-4895, the dacron tuft and a 190 gr. Lyman #311644 that I cast myself out of a mix 10 pounds of wheel weight metal, one pound of linotype, one-third cup of magnum bird shot (7 1/2 size as smaller shot has more arsenic in it.) and a 36" piece of 95/5 percent lead free solder. Bullets are sized .310 " and seated so that the bullets slightly engage the rifling. Velocity is about 1600 FPS. How accurate? From a Winchester M70 with 22" barrel, one a reasonably calm day I can get 1.5 MOA at 200 yards and 2.5 MOA at 300 yards if I do my part. I get basically the same results from a Savage 110S with heavy barrel using the same load. I loaded some up for a friend of mine who has a very expensive target rifle for match shooting and he slightly bettered my groups, but not by very much.
Anyway, hope that helps you out.
Paul B.
Naturally, YMMV but I think that'll give you a start.

if those are gaS CHECKED try 28 grs of 4895
and a tuft of dacron or some dryer lint.
the filler must touch both the powder and the base of your boolit.
if they are plain base the above loads will work.
as well as 10-13 gr unique.
10-12 gr red dot.
or 16 gr 2400.

the lyman cast bullet book has a bunch of loads too.