I would not use std SP primers in an AR. Pierced primers are usually the result. Some of it has to do with floating and non floating firing pins from what I have read. There have been post on here that claim Small Magum pistol primers are identical though. I have not found any specs to verify that. Many AR shooters claim you have to use tougher SR primers designated for use in AR's.I have not found that to be true in mine. Google Small Pistol primers in AR's and check out the AR and Tactical Rifle forum on this web site to ask the question. Warning though.You will get a lot of diverse opinions
