Bulk roughly measures the weight and unwieldiness of an item in Recon, with a rough equivalency of 1 bulk point to 1 pound. A soldier with a high bulk score will move slower and generate more noise, generally creating issues for a stealth mission. Extra bulk is generated by all weapons and equipment, though some more than others (i.e. an M3 vs. an M60).
To minimize bulk, first plan what you will need on your mission (a radio, for example), calculate roughly the kind of firepower you need to bring (higher bulk weapons tend to have more stopping power), and grab the lowest bulk items that satisfy your conditions. A tip for squads that stick together is to have similar bulk values among all soldiers (your radioman can pack a light gun, for example), so all your men move at roughly the same speed and stick together well.
Stages of Overencumbrance
Bulk will give a Ranger one of four potential Bulk ratings, denoted by either a Green, Yellow, Orange or Red indicator in their stat panel. These ratings will serve as an indicator as to the average overencumbrance of a Ranger in the field; however, these ratings will not penalize a Ranger's movement speed by any additional amount on top of their existing penalty or bonus due to their Bulk.
Currently, the threshold for a lightly packed Ranger is 25 Bulk - that is, 24 and below will denote a Ranger who is packed at his minimum Bulk rating. Due to the high Bulk of the mandatory PRC-77 Radio, it is only possible to achieve minimal bulk in a squad if the Radioman is equipped very minimally - usually with an M3 Grease Gun and light equipment such as a cleaning kit, field dressings, morphine or M14 AP mines.
Usually, most squadrons will use a loadout between 25 and 40 Bulk, which falls under the category of a standard weight loadout. However, for stealth missions, many commanders opt for all Rangers in their squad to maintain a loadout at 24 Bulk or less to maintain noise discipline and ensure extremely fast movement. Due to the higher bulk nature of heavy-hitting weapons and assault equipment, it takes extreme coordination and skill to formulate minimally bulky and yet effective loadouts for Overt missions. For this reason, almost all squads entering an AO with the goal of killing enemies or assaulting positions will be seen with a Bulk between 25 and 40.
Though unconfirmed, the believed threshold for moderate overencumbrance is 40+ to ~60. This stage denotes a Ranger who is above his average carry weight and is now burdened significantly more than a Ranger should be. This stage of overencumbrance is typically hard to achieve by itself; the only potential exception being assault loadouts which feature the Ammo Box due to its extremely bulky nature.
Finally, 60+ Bulk denotes extreme overencumbrance - the point where your Ranger is so heavily loaded that it's a miracle he isn't sinking waist-deep into the mud as soon as he leaves the Huey. This stage of overencumbrance is nearly impossible to achieve accidentally as the Bulk requirement is exceptionally high.