This is not so much a solution, but more of a checklist.
There a four achievements relevant to this checklist of the "29 shipped maps".
I've put abbreviations next to the name of each map to check off as you complete the requirements.
H10 = Waves 1-10 of Horde (can be achieved on Casual Difficulty)
H50 = Waves 1-50 of Horde (can be achieved on Casual Difficulty & does not have to be done in one sitting, you can continue from your previous last map completed however you will start with the default weapons)
MP = Play any multi-player game type
Win = Win any multi-player game type
I hope people find this helpful & good luck .
01. H10 H50 MP Win - All Fathers Garden
02. H10 H50 MP Win - Avalanche
03. H10 H50 MP Win - Blood drive
04. H10 H50 MP Win - Canals
05. H10 H50 MP Win - Courtyard
06. H10 H50 MP Win - Day One
07. H10 H50 MP Win - Flood
08. H10 H50 MP Win - Fuel Depot
09. H10 H50 MP Win - Fuel Station
10. H10 H50 MP Win - Gold Rush
11. H10 H50 MP Win - Gridlock
12. H10 H50 MP Win - Grind Yard
13. H10 H50 MP Win - Hail
14. H10 H50 MP Win - Highway
15. H10 H50 MP Win - Jacinto
16. H10 H50 MP Win - Mansion
17. H10 H50 MP Win - Memorial
18. H10 H50 MP Win - Nowhere
19. H10 H50 MP Win - Pavillion
20. H10 H50 MP Win - River
21. H10 H50 MP Win - Ruins
22. H10 H50 MP Win - Sanctuary
23. H10 H50 MP Win - Security
24. H10 H50 MP Win - Stasis
25. H10 H50 MP Win - Subway
26. H10 H50 MP Win - Tyro Station
27. H10 H50 MP Win - Under Hill
28. H10 H50 MP Win - War Machine
29. H10 H50 MP Win - Way Station