If you are still in need of 300 ICL Grizzly reloading advise, I may be able to help. I know there is not much out there for that caliber but I've had mine for about 35 years and it is my favorite rifle. I know of two other rifles that see use every year out in the field also. My Dad has one and a good friend also shoots one. All three rifles are re-chambered pre-64 Winchester model 70's that started out as 300 H&H. If you have one of the custom jobs that Juenke's built then you have quite a fancy gun ! They were good shooters too and made good long range rifles. I remember a photo hanging in their shop of a mule deer buck that Arnold shot at 700 plus yards.
Anyway, I do not load any of the lighter weight bullets in mine. My Dad and I both shoot 200 gr. bullets. Used to be we could only find 200 gr. Speer Spitzers and that is what we used for many years. Even they were special ordered. You can not hardly beat 200 gr. Nosler Partitions although I've loaded up some 200 gr. Accubonds lately and find them very accurate. Looking forward to the new (this year) 200 gr. tipped TSX's.
One thing I should mention is the case selection. You can use 300 Weatherby and 8mm Remington Mag factory cases by just running them through your sizing die and trimming them all to the same length. Pick the shortest one and go from there.
The 300 ICL was based on the 300 H&H case and you can make your own. This can be a pain as the 300 H&H case has a long taper with little shoulder. When you fire form the case it will have a very pronounced shoulder. You can load reduced 150 gr. loads but you will still lose many cases to splitting necks. The best way is to prime the factory case and load 25 grains of Red Dot or Bullseye and fill the remainder of the case with Cream of Wheat (dry). I was told to put a little wax (car wax) over the mouth and then fire in your rifle. I could not figure out the wax part and just held the gun upright and carefully loaded each round into my gun and fired them. I've made a couple hundred using this method and have not lost a one. The new case will have the most capacity of the three and you may be able to load it a little hotter (or not). Run theses through your size die and trim them to the same length. Again, find the shortest one and trim them all to that length. Max case length is 2.85 inches. Trim cases to 2.75 inches although I don't think you will find any that even come close, just make sure they are all the same length.
It is best not to mix case types when working up a load. The easiest is the 300 Weatherby case from Remington as these are usually cheaper than the Weatherby (Norma) made cases. You can just load these up to full charge and fire them. In my gun, they are still accurate. Your hunting loads should all be at least once fired to gain the most accuracy. Size and trim cases each time you fire them.
I trim to 2.815 and my OAL is 3.610. Make sure these will fit in your magazine.
Loads in my gun are : 200 gr. Accubond (or Nosler Partition)
78 grs. IMR 7828
215 Federal primer
This load is a Max load and is right at 3000 fps.
200 gr. Accubond (or Nosler Partition
76 grs. H 4831
215 Federal primer
This load is a Max load and around 2900 fps
My Dad's gun will take another grain of powder and not show pressure signs. Each gun is different and you need to start 3 to 4 grains lower on the powder and work up.....carefully ! You will need a micrometer. To check for signs of pressure, look at the base of the case for imprints of your bolt face, flattened primers, and measure the belt on the case. If any have expanded over .532 throw them away and back off the load by at least one grain if you have been coming up 1/2 gr. at a time.
My friend shoots 180 gr. Nosler Partitions only. He does not reload. His brother loads up his ammo and uses 76 grs. IMR 4350 with a large rifle magnum primer. That is all I know about his load. I would guess this also a Max load.
The thing with Juenke Saturn was that each gun was a custom gun with custom loads designed for each rifle. When you bought a ICL from them, they would work up specific loads for that gun and that gun only. I have a copy of their gun line and a few loads for each of their calibers. They did not go into great detail about loads. The only powder they used was IMR 4350 for the 300 ICL Grizzly.
There is one 150 gr. load and it is 80grs. 4350 for 3590 fps. I would guess this to be a Max load also as they really touted their velocity figures.
I hope all this helps. PM me if you need more help or have more qustions