I use the Stoney Point guide on my AR's but I believe it has been acquired by Pro Shot It works well for me. They come in different sizes for different fore sizes but the Pro Shot above will cover all your bases nicely. I hve had a couple of the solid Delrin types but I have encountered fitment issues in some uppers with some brands. My original one was from Midway, it was blue, and I had some uppers that were very tight.