Ok, I am new to reloading and I know that there are two sizes of primers (large and small) and two primer set ups..(rifle and pistol) along with two strengths (regular and magnum) So I know that rifle primers have thicker cups which take more force to ignite.. I just seen a you tube video that freaked me out.. It said that some primer brands for rifles are designed for bolt action and do no have a thick enough wall for semi autos with free floating fire pins causing slam fires... (such as a AR15).. Is this true? It has freaked me out out.. I thought all rifle primers in proper size were safe to use on my semi auto weapon..