WGR, you shouldn't have a problem if this is in your H&R Target, the thinner 30-30 brass will allow you to load up to 375 Win velocities with less pressure due to the increased case capacity. Read Marshall Stanton's reply in the link below.
I'm using the 2.125" long Starline 38-55 brass, (I like properly headstamped brass
), my Target chamber will accept the .380" cast bullets required for the 38-55 Target to shoot accurately, 30-30 brass will just be shorter, I tried some 375 Win brass that I'm using for a 30-30AI, it's too thick to chamber a round loaded with a .380" bullet. I'm loading the Chey-cast .380" 325gr Snover bore rider bullet to 2.850" COL, and the .380" 270gr Mt Baldy to 2.555", those COLs are to the lands in my rifle.
For those that aren't aware, the H&R Target uses the same SB2 frame as Handi and Ultras that are factory chambered in 270 Winchester and other high pressure chamberings.
Tim
http://shootersforum.com/showthread.htm?t=2137&highlight=.375+win