4130 is chrome moly which is pretty soft. The description says it’s 4140 steel. The mil-spec standard is 4150. the last two numbers are the carbon content. More means harder and more resistance to wear so the 4140 barrel will not stand up to the abuse the 4150 will. 4150 will stand more heat (100 degrees more according to specs), so sustained fire is less likely to hurt the barrel.