Any game giving you an achievement to stomping limbs off deserves more credit than it gets. Anyways.
This can easily be gotten within the first 6-7 chapters, doing things your sick mind already does. Go around stomping every single dead body to tiny arm bits. Human bodies can nag 5 limbs if they're still all put together, and any enemies with limbs still attached after death can be stomped on to get even more limbs. Probably the funnest achievement ive ever done.
As a side note, if your trying to get the Plasma cutter only achievement, this achievement will be easy as pi. Plasma cutter is by far the fastest limb cutter in the game, cutting a normal necro's limbs in 1-2 shots. Sure the line gun is good, but its costly to keep ammo up, and it only gives you a tiny achievement, unlike plasma cutter which nags a pretty big achievement.