Also:

http://backpack.tf/profiles/76561198353843277#!/compare/1494028800/1494288000

http://backpack.tf/profiles/76561198301631710#!/compare/1494720000/1495065600

The sweets added with the Copper's in sale 1 are closer to 10 keys, but the PKS Aussie Scattergun in your minigun mini was easily worth a few keys more at the time of the sale (2 months ago), so it evens out.

There are 3 other sales:

The one posted above by Joxu for 20 keys pure

http://backpack.tf/profiles/76561198353843277#!/compare/1494028800/1494288000

http://backpack.tf/profiles/76561198088005903#!/compare/1494201600/1494288000

Sold with ~1 key in sweets for a Steaming Mohawk (59)

http://backpack.tf/profiles/76561198301631710#!/compare/1494460800/1494633600

http://backpack.tf/profiles/76561198147059742#!/compare/1494547200/1494633600

http://backpack.tf/profiles/76561198084205929#!/compare/1494547200/1494633600 ----- The Mohawk was traded quickly for the HG Mirror + sweets

GBH Capotain (30)

http://backpack.tf/profiles/76561198241375086#!/compare/1495497600/1496102400

http://backpack.tf/profiles/76561198016530188#!/compare/1496102400/1496188800

So there are sales for 20, 24, 30, 50+. I could see this getting a 20-30 range, but honestly, 24 is close enough.