Open your console while ingame by pressing ` (the key below ESC)

Then enter the following commands individually:

cl_ragdoll_dismemberment 1
cl_ragdoll_gib_shadows 1
cl_ragdoll_gib_freeze 0
cl_ragdoll_dismember_bullets 1
cl_ragdoll_dismember_bullets_fraction 0.5 (the higher the number, the easier to break limbs, I found the previous number 1 to be a bit too sensitive to my own preference)
cl_ragdoll_dismember_limb_limit 4

There are many other guides about creating an autoexec.cfg under your installation folder.

In short, this allows you to incorporate multiple command lines automatically at game launch.

So for this method, simply copy paste the following commands into your autoexec.cfg

cl_ragdoll_dismemberment 1
cl_ragdoll_gib_shadows 1
cl_ragdoll_gib_freeze 0
cl_ragdoll_dismember_bullets 1
cl_ragdoll_dismember_bullets_fraction 0.5
cl_ragdoll_dismember_limb_limit 4

My specs:
i7 7700K @4.3Ghz
16GB DDR4
SSD (1X for WIndows, 2X for games, other HDDs for other stuff)
GTX980

No performance hit from these tweaks to my environment.