I belong to a couple forums and several gun Facebook pages (these are typically a joke) and all the time I see "custom" AR's for sale. I'm personally not a fan of AR's so I don't follow them closely but I don't consider most of these guns I see to be "custom". I consider a custom gun to be built by a reputable builder using parts that you can't buy off the shelf. This is just my opinion and I'm curious to see what other peoples opinions were on this matter.