That rifle looks like a possible military match rifle from 1957, but what branch used it - is unknown. It is way too nice to have ever been used as an actual sniper rifle in Vietnam. It still has its Winchester barrel, which is interesting. The scope looks like a legit USMC target rifle scope, but that scope was not the kind used in Vietnam. For the price being asked, I'd send CMP a check for $25 to see if was sold/auctioned by them in the past. I'll defer to CplNorton who has researched the M70 topic at the USMC archives. I lean towards a late 1950s match rifle for high-power matches.