AR-15 SBR fires factory ammo fine, but half my reloads, all from the same batch, jam and won't chamber. Rounds fit the RCBS chamber gauge fine, which measures headspace, diameter and COAL. They fit loose so there is slack in the casing diameter. 110gr V-Max bullets seated below max COAL. When I mic. the cartridges they all measure under SAAMI specs for length, diameter etc. But the rifle doesn't like them. I just cleaned the Aero Precision AR and checked well for grit etc. that could be the cause. And like I said factory ammo chambers OK. I guess I could just keep cranking down the RCBS Small Base resizing die until the shoulder bends, but that seems a little hap-hazard. Any Ideas? Could it be the PMAG magazines? They all chamber fine with factory ammo, and with .223/556 reloads in my other rifle.