The .225 was based on the .30/30 case, with a rim the same thickness and diameter as a ..30/06 rim. However there is no extraction groove. It was referred to by Winchester as a semi rimmed case, but looks for all the world like a rimmed case to me, although it does normally headspace on the shoulder.
One could form .225's from .30/30 brass, but it would involve lathe work to reform the rim as well as forming work on the body of the case.
Proper .225 brass can be found, and it is worth the trouble to look for it, compared to the hassle of forming it from .30/30 brass.
