Sale 1:

Sold for Australium Grenade Launcher (~13)

Seller: https://backpack.tf/profiles/76561198023139465#!/compare/1539043200/1539129600

Buyer: https://backpack.tf/profiles/76561198101372054#!/compare/1537142400/1539129600

https://backpack.tf/item/2344718995

X = 13

Sale 2:

Sold for 12 keys

Seller: https://backpack.tf/profiles/76561197996095002#!/compare/1541289600/1541376000

Buyer: https://backpack.tf/profiles/76561198130439878#!/compare/1541203200/1541376000

https://backpack.tf/item/2344718995

X = 12

Sale 3:

Sold for ~11 keys in pure/metal

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1538870400/1538956800

Buyer: https://backpack.tf/profiles/76561198066693591#!/compare/1538784000/1538956800

https://backpack.tf/item/2344718995

X = 11

Sale 4:

Untraceable

Seller: https://backpack.tf/profiles/76561198169652473#!/compare/1538870400/1538956800

Buyer: https://backpack.tf/profiles/76561198023139465#!/compare/1538870400/1539043200

https://backpack.tf/item/2344718995

Sale 5:

Untraceable

Seller: https://backpack.tf/profiles/76561198061779536#!/compare/1542499200/1542585600

Buyer: https://backpack.tf/profiles/76561198079726942#!/compare/1542585600/1542672000

https://backpack.tf/item/2344718995

Sale 6:

Untraceable

Seller: https://backpack.tf/profiles/76561198261003871#!/compare/1542585600/1542758400

Buyer: https://backpack.tf/profiles/76561198057308825#!/compare/1542326400/1542672000

https://backpack.tf/item/2344718995

Sale 7:

Sold for Roaring Rockets Fubar + ~2 keys in items

Seller: https://backpack.tf/profiles/76561198101372054#!/compare/1539820800/1540684800

Buyer: https://backpack.tf/profiles/76561197996095002#!/compare/1540512000/1540598400

https://backpack.tf/item/2344718995

Way too low now.

Sale 8:

Sold with 12 keys for Purple Confetti Kiss King

Seller: https://backpack.tf/profiles/76561198130439878#!/compare/1541548800/1541721600

Buyer: https://backpack.tf/profiles/76561198242646048#!/compare/1541721600/1541808000

https://backpack.tf/item/2344718995

Using on the King.

Sale 9:

Bulk for Kill-a-Watt Rotation

Seller: https://backpack.tf/profiles/76561198043753037#!/compare/1542412800/1542499200

Buyer: https://backpack.tf/profiles/76561198164036774#!/compare/1542412800/1542499200

https://backpack.tf/item/2344718995

Sale 10:

Bulk for Insomnia Nappers

Seller: https://backpack.tf/profiles/76561198164036774#!/compare/1542412800/1542499200

Buyer: https://backpack.tf/profiles/76561198061779536#!/compare/1542326400/1542499200

https://backpack.tf/item/2344718995

Sale 11:

Sold with cheap items for Logo Conquistador

Seller: https://backpack.tf/profiles/76561198079726942#!/compare/1541721600/1542585600

Buyer: https://backpack.tf/profiles/76561198261003871#!/compare/1542499200/1542585600

https://backpack.tf/item/2344718995

Can be used on the Conquistador

Sale 12:

Sold for Dead Presidents Vintage Merryweather + Killstreak Festive Shotgun

Seller: https://backpack.tf/profiles/76561198066693591#!/compare/1538784000/1538956800

Buyer: https://backpack.tf/profiles/76561198169652473#!/compare/1538870400/1538956800

https://backpack.tf/item/2344718995

Can be used on the Merryweather. Will either fit into the range or be excluded if used here.

Marketplace Sales:

Sold for $26.96 & $16.05 on marketplace

https://marketplace.tf/items/95;5;u60

https://manic.tf/keyprice/?at=2018-09-25 - $16.05 / $1.83 = 8.77 keys

https://manic.tf/keyprice/?at=2018-11-08 - $26.96 / $1.77 = 15.23 keys

X = 15

X = 9

Sellers:

https://i.imgur.com/f994RRU.png

https://backpack.tf/item/2344718995 - 15 keys

https://backpack.tf/item/1899495793 - 16 keys

Sales at:

9

11

12

13

15

Highest buyer currently is 11: https://i.imgur.com/kcvHkS9.png

Excluding 9 and 11.

Going with 12-15.