So, i beat the game on hard without knowing you should do the pistoleer achievement first.  Now i'm stuck.  I want to totally and completely delete all game data from my HD.  I went to the memory part of system settings and deleted this game's folder.  All that was in it were my save games. 

I go back into the game and low and behold, i can still continue where i was and it still knows i've beat it on hard.  So, that means there is a game file somewhere on the system i cannot see or do anything about, right?  Has anyone been able to find this file, delete it,  and basically 'start fresh'?  I really need to know as i have to return this game soon. 

Thank you

If you don´t have a memory card to move your profile, maybe you can clean the cache by pressing Y on the HD symbol and then press X,X,Left Bumper, Right Bumper, X,X

Send 'radfannybandit' a message and ask him. He was glitched on this very same achievement and sent me a message telling me a method he found to reset the game so he could get the achievement. I forgot the method myself and unfortuneately...the message he sent me has expired and been deleted.

I remember his method involved having two profiles on the 360 and you just switch really quick between them at a certain point when you're loading.

Anyways...he knows what to do. 

can someone please tell me how to get pistoleer achievement. i already beat the game on hard yet i can't get the pistol achievement.

Some people are glitched on this achievement and need to use the technique radfannybandit found to get it.

If you're not glitched...just move slowly through levels (you can do it on easy) using the pistol. Hang out in every area until you're sure no one else is going to show up. A lot of guys will eventually show up if you wait for them. If you run out of pistol ammo...use another gun until you pick up more.

Also take the extra second or two to go for head shots. This will save you much time as it can take 4 - 5 body shots to kill an enemy and only a single head shot. --It will also make your pistol ammo last a lot longer.

Do all that and you'll get the achievement in only one or two levels.

There is a way to "fix" the glitch and radfannybandit helped me to get it. Took me a while to understand the steps but it worked for me. My achievement timestamps can show that. To understand the problem as why deleting game data does not work it is because the root cause is that the game data, ie kills, missions, levels, etc., are stored on the Xbox Live servers rather than your individual xbox console. For instance I completed the game on hard on one xbox and when I went to a brand new 2nd xbox console all my stats were there - bizarre - not really as the stats are on the Xbox live servers. If you are not too far into the game I would sadly recommend doing all the easy levels first prior to normal/hard levels.