I just realized that there's another thread where proof is asked for so here's what I can find.
"By Aestil on 10/26/2006 (Patch 1.12.2)
This gun is attainable by completing all of the hunter quests in STV. You get a final quest to kill the master of all the beasts or something. There is also a bow which can be rewarded.
The main reason this gun is amazing is that it is attainable by a lvl 29 twink. And because the gun is a high lvl, a +40 friend can attach the +7 dmg scope to it."
http://db.vanillagaming.org/?item=17687#wh-comments This is a comment from from vanillagaming about the gun being used in patch 1.12.2
Next is a guide for 20-29 twinks that lists the gun as bis
"Range: Ironweaver / Master Hunter's Rifle [+5/+7range dmg]
Ring: Seal of Sylvanus / Plains Ring
Ring: Basalt Ring of Monkey / agility (WSG Ring) "
http://www.blizzardguides.com/20-29_bg_warsong_gultch_twink_guide.htmlThe guide itself doesn't have a date (as far as I can tell). It does however talk about talent builds that were in 1.12.2, but changed in later patches which can help to date it (1.12.2 or before). A specific example is the warrior spec
"0/11/9
5/5 Cruelty
5/5 Unbridled Wrath
1/1 Piercing Howl
5/5 Shield Specialization
4/5 Iron Will "
In patch 2.0.1 Shield Specialization was moved to a tier 2 talent and Iron Will was changed to an arms talent.
2.0.1 talent tree:
http://www.wowprovider.com/Old.aspx?talent=2006080_11.12.1:
http://db.vanillagaming.org/?talent#LHere's the other thread in case this should be merged
https://forum.nostalrius.org/viewtopic.php?f=45&t=10550&p=74148&hilit=master+hunter#p74148Edit: Here's a video showing a 29 hunter with the master hunter rifle (you can tell from the model in game and the description of the video). Based on the post date it's from before Jul 29, 2006 and based on the raid chat in game (it's before cross-server battlegrounds), the video is from before patch 1.11.2.
https://www.youtube.com/watch?v=wEg8DxSSYyEI went through the next several patch notes and the only mention of changing the quest is after the TBC release, and that was only to nerf the gun, not change the level requirement.