Bullet proof may be a western thing. When you palmer a hackle which is to wrap the hackle around the hook from back to front the fish that have teeth will cut through the hackle and it will come unwrapped ruining the fly. So to correct the problem you make a dubbing loop on the back of the fly and put the hackle inside the dubbing loop and spin it inside the loop and what you have is a hackle that is totally wrapped in thread then you palmer it. Now when the hackle get cut it will not come unwrapped. Hope this helps.