I know i told some of you to use the IGN Kid River file, but don't bother, yes it does get you some of the acivements but I noticed that I was not getting a lot of scores for my kills.
It took me 63 min of murdering to get this which is not long at all.
Use the belowDownload this by IXI JoHnnYB IXI 1.Mio Points EASY
Make sure the Mission is on Corvette
and the Game difficulty is on Legendary
otherwise you wont get the achivements.
A few tips, Keep the needler it will help in the early stages with your multi kill scoring, try and find the magnum so you can get the achivement for it.
This is the fire fight achivements list(image credit goes to xbox360achievements)
And this is what it will look like after the hour
Hope that helps guys