I noticed that it was only being listed with cast bullets. Misprint? Accurate data?
its not a misprint, and its as accurate as the rest of your data from the same source.
Did you happen to notice the listed velocity? Its WELL below regular .300 Mag speed. it's a reduced load, intended for plinking, and possibly small game.
You can make and use such ammo but you must be EXTREMELY CAREFUL!!!
I was doing that, or more accurately THOUGHT I was doing that nearly 50 years ago loading Unique under 173gr cast slugs in the .308 Win. I mistakenly loaded a grossly overcharged case, and nearly blew up a Remington rifle.
Got hit in the face with hot gas, and the bolt was locked shut solid. Gunsmith actually slightly bent the bolt handle getting it open, and had to use a chisel to get the fired case out of the chamber. The case head had expanded enough that the primer fell out, there were 3 visible cracks in the case web and there was a "belt" of brass swaged on the case body just ahead of the extractor groove. Looked it up, and according to the books, those signs indicated somewhere between 90-110,000 psi.
Gunsmith told me I was lucky, and that Remington only proofed the rifle to 80k psi...
Broke the extractor, and pin, ejector pin, safety pin, and bolt stop pin (from the vented gas. No damage was found to the bolt body, lugs or receiver, the rifle was repaired and I still have it, but as I was told, I GOT LUCKY!!
I haven't messed around with Unique as gallery loads for rifles since then.
Done right, they work and are safe (there are a few things you should do help ensure that that usually aren't given in load data tables) done wrong serious risk of KA-BOOM!!
You can make ammo for your .300 Win Mag that will let you shoot squirrels and bunneys without blowing them up. It won't shoot to the same zero as your deer and elk ammo, so you'll have to sight in the rifle for the light load if you want to hit anything, and then rezero it for big game.
For most people today, its easier (and safer) just to use a different gun (like a .22LR) for small game and save the big guns for the big critters.