Sinclair International's 30 Caliber Stainless Steel Neck Turning Mandrel is sized at 0.306", which is .002" under bullet diameter for precision reloading.
The mandrels are made from high-grade stainless steel, with the option of carbide mandrels that offer even tighter tolerances.
Large caliber mandrels (35 to 50 caliber) are compatible only with the Large Caliber Expander Body and NT-5000 Turning Tool.