How to attach grenades to the walls

I don't believe that Gears of War 3 pays attention to what body part is being shot. A shot to the head obviously does more damage with certain weapons like you said. Getting shot in the arm, leg, or chest should do the same damage with most weapons.

Besides the head, GoW 3 doesn't have specific damage modifiers to certain body parts.

On a side note, when I was searching for a chart for proof of this, I found a chart of the weapons and their damage, fire rates, and clip size. This could be useful in some way to you:

http://www.ign.com/wikis/gears-of-war-3/Weapon_Statistics_Chart

Active reloading allows you to reload the gun faster than normal. This is achieved by tapping to reload and the tapping reload again when the reload tracker is anywhere within a grey bar highlighted on the reload gauge.

A "perfect" active reload is achieved when you tap the reload button within a much narrower white bar on the reload gauge. This fills the empty rounds in your click with special shots, indicated by flashing ammo symbols (for guns with bullets). The damage per shot is also increased by around 8%. (Except for the Scorcher).

These special shots have differing effects for some guns (paraphrased from above link):

• Hammerburst II - Gets only 15 rounds in its magazine instead of the usual 17.
• Boltok - Rate of fire increase.
• Torque Bows - Charge up faster.
• Boomshot - Receives an aftershock of mini explosions.
• Scorcher - Receives a range increase.

As wilerson noted in the comments, if you click reload anywhere outside of the white or grey bar, before the reload is complete, then you achieve a "failed" reload. This confers no bonuses and increases the time it takes to reload the gun, such that it would have been faster to do nothing after starting the reload.

To summarise: Any active reload will cut down reload times. A perfect reload will grant bonus damage and some extra effects depending on the type of gun. A failed reload will increase reload times.