Bushing without reducing pin diameter accomplishes little or nothing unless the hole is way over-sized. With a .068 pin, reduction to .0625 could make a difference but I think I would be inclined to check the shape of the firing pin tip first. If the tip is flattened, with a slightly sharp edge, it will tend to cause primers to blank and I have seen this on Stiller actions. Re-shaping the tip to a smooth, hemispherical shape will often cure the problem.