I need to make myself a plane to cut the groove, but in the meantime...
I will lay out the position on the stock and draw the outlines. Then, I take a yardstick, and clamp it down on the stock along either outline, and take a knife and score along the line. This helps GREATLY in preventing wood from chipping out the side of the groove. Then, I just gouge it out with an appropriately sized round gouge. I have a little adjustable square that I use for a depth gauge. When I get much of the bulk of the wood gouged out, I then take a piece of 3/8" round steel stock that has the edge cut off sharp, and use it for a very effective scraper to clean up the groove pretty quickly. Also, the steel rod is rusty, and I can lay it in the groove, and rub it back and forth and it works well to show me the high spots.
It doesn't take nearly as long as you might think.