Dead Space 2

Use a Contact Beam on any Necromorph but hold LT (to aim) and Press RB (to knock it down with it's ALT-fire). Now it should be on the ground. Quickly, charge the Contact Beam (hold RT) and kill it before it gets up (let go of RT)!

IGN has special video for dead space 2 achievements.
In this video it will show you how to get "My boom stick","going for distances" ,"taste of your own medicine","c-section" ,"elevator action"(this is a secret achievement) and "collect peng"

But we're here for the "c-section" achievement. Its pretty easy achievement to get all you have to is buy the "contact beam" for 11,000 credits and buy one pack of ammo just in case you mess up. Find a slasher and quickly use the alt-fire(RT+RB) to knock it down and quickly charge up and discharge the beam before the slasher gets back up.

This achievement has to be done on normal difficulty or higher since the contact beam does a lot of damage from the get go and will always kill your target on the casual diffculty. Another thing to keep in mind when going for this achievement is that you should have some energy in your stasis because more often then not the Necromorphs will get up, after having hit by the altfire, before you can charge up the primary fire. The uploaded video gives far more detail on how to get this achievement including where to get the schematic for the contact beam along with all the information I listed above. All credit for the video to the Achievement Hunter Community and MPKlookie.

Cheerio everyone

I know this is "late to the party" so to speak but I'm going through and doing some mopping up. This is how I did it and it worked perfectly because I'm on 2nd play through and have a fully upgraded Contact Beam and the stasis was preventing them from being knocked back PLUS it was killing them instantly. So if this is you and you're having trouble, try this.
I played on casual until I got to wear Isaac sees the ships taking off through the huge windows (ch. 2) A few minutes later you'll come across you're 1st work bench, PASS IT UP. Go through the door, kill a few necros and there's a save station right there to the left. Save. Change difficulty to Zealot, go back to the bench and unload all the power nodes from Contact Beam. I reinserted for capacity and reload because I wasn't sure it would work but it did the 1st try so you don't even need to do this.
Go back and PASS by the save station and go through the door where you'll be in a hallway. To the right there's some necros terrorizing citizens through a busted wall, you'll see one morph and then walk off to the left of the screen. Turn back and face the hallway, about 15 seconds later that same necro comes for you. Use your Alt beam then charge and kill, you dont even need to stasis it 1st. Then if you're going for more mop ups like I was, just reload the check point and it'll take you back to where I 1st told you to save and your Contact will be back to full upgraded and back on whatever difficulty you were playing on. Good luck, hope this helps. It took less than 5 minutes when I got to the area.