Probably Blackjack era or Kabar era. Take a look on the back of the sheaths, granted they may be later sheaths, but usually they go with the time frame the knives were made, maybe. before Blackjack, they were made in Richmond, Va and my sheath states same, of course mine is a double edged desert Bowie with tan chord wrap made at around the tine of the first Gulf War. Hope you can get some pics up. Are the guards of yours a rectangular steel guard or the slightly curved brass guards? Sounds like they are modern model 4s. I believe the blackjack ones had made in effingham in the back but could easily have worn off too. Use the search function here to see older threads or pics may help too.