In the Fourth Circuit, 3 judges have D/R or R/D appointments (i.e., CJ Gregory, Traxler & Floyd). 8 of the 18 have R or R-only appointments. 7 of the 18 have D or D-only appointments. The chances of drawing a strictly R-only panel of judges are 8/18*7/17*6/16 = 7%.
Not that it matters.
Did I tell you?: only 7%.
Seth runs the numbers. His post is worth reading in full, as usual.