FWIW to anyone, I just made one using the pattern Colorado Clyde posted. It's,,,, serviceable. I will make another based off that pattern, with a few changes. 1st, for a rock lock it needs to be bigger (mostly longer), second, it needs to be stitched up with the intention of not turning it inside out or something needs to be done about that long seam down the center of the barrel end of the cover. When turned so the sewn welt is inside the welt hits the barrel making it tough to get a seal there. I will cut my next one longer as well as a lot wider. Thinking if I cut it way oversize width wise, I can recut it after sewing so that the seem is off center and drops in next to the barrel. I'm also toying with the idea of cutting two triangles out of the barrel end, each half the width of the one the pattern calls for and spaced so each seam falls on either side of the barrel. Also, the rear welt should be a little longer, for a rock lock. Other than the front welt hitting the barrel it think this pattern would work well as is for a percussion lock.