Display the table of demon hunter rapid fire gear first. In the table, AS stands for Attack Speed, and BDPS is Base Damage Per Second for short The growing rate refers to the condition when your attack speed is at lower limit.
Attack speed lower/upper limit explanation: When you reach an attack speed, the damage will increase to actual speed upper limit. For example, gear 2 fire support (the most used rune in the first four) rapid fire AS is 2.0-2.5. And as long as your AS reach 2.0+, the actual damage from fire support is the same with AS 2.5, and base damage per second is 1095%.
If your AS is 2 and DPS is 300 thousand, in fact it has a growing rate of 25% damage by using fire support. That means your actual output is 375 thousand. Meanwhile, the lower the attack speed, the slower hatred cost. In other words, AS 2.01 and AS 2.49 fire support has no difference in damage but hatred can last longer with 2.01.
The conclusion is, controlling the AS a little higher than lower limit is very helpful to rapid fire in battles.
We mainly talk about Bombardment next.
Gear 0, lower limit 1.538
This gear is so-called infinite rapid fire. The cost of hatred is slower than generating, so Bombardment is enough for resource. Manticore can reach this AS easily but the output required is very low. Here AS 1.10 crossbow is recommended. And the additional 40% AS can be get by Inna set pants + Inna set ring + Mempo of Twilight + Dead Man's Legacy. Gloves and amulet can give up dph and ehp.
Gear 1, lower limit 1.667
This gear can realize infinite rapid fire in general. Manticore is proper here. Change any one of Inna set pants + Inna set ring + Mempo of Twilight to the witching hour to improve whole property.
Gear 2, lower limit 1.818
Usually it needs a skill like Grenades or Bola Shot to keep hatred from gear 2. Manticore and Mempo of Twilight + Dead Man's Legacy + Inna set ring + The Witching Hour reach gear 2 is not a problem.
Gear 3, lower limit 2
This gear is usually for two-handed demon hunter. The output is wonderful. AS 1.221 Manticore needs additional 64% attack speed while AS 1.21 needs at least 66% to meet the requirement. So if you want to play AS 2+ shining demon hunter, choose 11% Manticore as possible as you can instead of 10%. In general, it needs another 7 items to reach gear 3. Mempo of Twilight + Dead Man's Legacy + Inna set ring + The Witching Hour has AS property at most times, and the rest can choose 3 from gloves, amulet, pants and bracer.
Gear 4, lower limit 2.222
This gear is hard to balance equipment. Calamity is slow but Manticore is too far away. On the condition of using Stone of Jordan, Mempo of Twilight, amulet, gloves, Lacuni, Witching Hour, Inna ring, Inna pants and Dead Man's Legacy together improve AS 83% at most. 10% AS Manticore 1.21*1.83=2.2143 is not enough for gear 4 while 11% Manticore 1.221*1.83=2.234 does. The 8 items can be not one less. If you can do that, the damage would be terrible.
Gear 5, lower limit 2.5
Calamity needs 43%+ AS to reach gear 5. It's not difficulty to do that. The deficiency of dph can get by choosing belt and shoes with element damage. The rest equipment you can refer to gear 0.
Gear 6, lower limit 2.857
The main gear for Calamity rapid fire. Equipment select you can refer to gear 3.
Gear 7 is too hard to reach and is meaningless to operate though you make it in AS.