I was told by a person at Green Mountian they made the 17 barrels for NEF and that they were 4140. Could not prove it either way, but my 17 remington barrel didn't blow up. NEF 17 barrels are a 1 in 9 twist, so they are good up to 30gr bullets in a CF, and the barrel blanks GM sell are also a 1 in 9 twist and made with 4140, check their web site. Larry