From Team Fortress Wiki
The Walkabout allows the Sniper to walk at normal speed while scoped. The downsides to this ability are that the Walkabout does reduced damage, cannot deal critical hits on headshot, and cannot charge its shots for increased damage.
The Walkabout would have been available to Snipers after attaining a certain number of achievements. It was, however, replaced by the Huntsman because the development team thought it made the Sniper function too similarly to players wielding sniper rifles in the Counter-Strike series of games.
Text relating to the Walkabout can be found in tf_english.txt
The Walkabout's name:
"TF_Unique_Achievement_SniperRifle" "Walkabout" // ADD THE
Some unique attributes likely related to the Walkabout:
"Attrib_ZoomSpeedMod_Disabled" "No move speed penalty from zoom"
- "Attrib_SniperCharge_Per_Sec" "+%s1% charge rate"
- "Attrib_SniperNoHeadshots" "No headshots"
- "Attrib_SniperZoom_Penalty" "%s1% zoom reduction"
- "Attrib_SniperNoCharge" "No zoom or damage charge"
- The name of the weapon is derived from a rite of passage, of the same name, in Australia's Aboriginal culture.
- The Walkabout's no headshots and increased charge rate attributes were later recycled for the Sydney Sleeper.
- There is a weapon called the Walkabout with the same attributes in the Advanced Weaponiser.