style=”text-align: left;”>Receiver slop is the common name for the amount of movement between the upper and lower receiver of the AR-15/AR-10 weapons platform. Although it is commonly accused of causing functional or accuracy issues, it is in reality just an annoyance and side effect of mating Mil-Spec parts. No two AR-15 parts are ever exactly the same. Mil-Spec is the set of military specification governing the tolerance or amount +/- that a part may be from ideal, while still being a good part. Most weapons manufacturers actually hold their weapons and parts to a much higher standard than true Mil-Spec. For example, a true military spec weapon may be missing up to 20% of its receivers’ anodizing.