How much damage can a character deal in a single round using a ranged weapon?

Question

Rules and restrictions:

1. Spells are allowed, as long as it doesn't deal damage on their own (e.g shooting one arrow and using your bonus action to deal damage with a Blade of Disaster);
2. Damage can't be dealt to the character him/herself or any of his/her allies, although, since it's theoretical, something that has a chance to harm them, but can also damage enemies is allowed;
3. There is not an specific limit to the number of targets, if you need a lot, you may have them, as long as the number doesn't go too far (such as in 500 tiny flying creatures for Ranger's Volley); NOTE: Please clarify how much damage each target will be taking
4. Again, not an specific limit to how many teammates you may have, but stacking a buff from an certain build is not allowed;
5. Separating the damage in 3 categories would be much appreciated, although not needed, as just showing each step during damage calculations is enough: 1st. No magic items, boons nor other buffs; 2nd. With magic items and boons, no other buffs; 3rd. Everything included.
6. Only official content is allowed, and anything else not covered in these limits can be assumed to be allowed

Answer 1

With all the buffs we can exceed 20,000 average damage, but let's start at the beginning:

With no buffs

1,043.75 average damage [1,709 max]

Bugbear Gunner

Our archer for the no buff, no magic version is a Bugbear Fighter (Battle Master) 12/Rogue (Assassin) 5/Ranger (Gloom Stalker) 3 with a hunting rifle and purple worm poison on each bullet. Our allies are an 14th level Fighter (Battle Master), a 7th level Paladin (Oath of the Sentinel), a 6th level Warlock (The Fiend), and a 2nd level Wizard (Chronurgy Magic). This provides the following damage elements:

• 4 attacks per action via Extra Attack and Dread Ambusher.
• Action Surge to take the Attack action again.
• 1 attack via Commander's Strike
• These 9 shots are possible since we can reload our hunting rifle once with our bonus action.
• 5 ASIs for the Athlete, Gunner, Martial Adept, Piercer, and Sharpshooter feats
• 7 d10 Superiority Dice (5 from levels, 1 from Superior Technique, 1 from Martial Adept)
• 1d12 extra from the Commander's Strike
• 2 Sneak Attacks (3d6 each)
• 2 Dread Ambusher Attacks (1d6 each)
• 9 Surprise Attacks (2d6 each); our Paladin, Warlock, and Wizard help us go first
• Every attack is a critical hit from Assassinate
• One die gets rerolled with Piercer
• Purple Worm Poison damage (doesn't benefit from the critical hit)

Altogether, our average damage is as follows:

$$9*((1*6.75)+(4*5.5)+(4*3.5)+(12*3.5)+10+5)+7*(2*5.5)+2*(6*3.5+2*3.5)+1*(2*6.5) = 1043.75$$

With magic items and boons

1,889.75 average damage [3,203 max]

The Oathbow

The previous build essentially works as is with one deviation: we replace our hunter rifle with an oathbow, use arrows of slaying and attune to the Book of Exalted Deeds and the Eye of Vecna for 3 major beneficial properties of 1d6 extra damage each. This changes our base damage from our weapon from 2d10 to 6d10 + 1d8 + 3d6 and gives 3d6 extra damage per attack.

As such, here is our average damage:

$$9*((1*6.75)+(11*5.5)+(3*4.5)+(6*3.5)+(6*3.5)+(4*3.5)+(12*3.5)+10+5)+7*(2*5.5)+2*(6*3.5+2*3.5)+1*(2*6.5) = 1889.75$$

With the buffs

23,668 average damage [40,768 max]

The Characters

If we are able to use buffs, a different build is in order. We should now be a Duergar and here are the classes of our new build:

• Fighter (Eldritch Knight) 3 ---------------------------------------------------------- for Superior Technique, Action Surge, and the wizard spell list
• Rogue (Assassin) 17 --------------------------------------------- for Assassinate, the Martial Adept, Metamagic Adept, Piercer, and Sharpshooter feats, and Death Strike

...here are our magic weapons:

• longbow
• Book of Exalted Deeds
• Eye of Vecna
• Hand of Vecna
• sword of the paruns
• 14 arrows of slaying
• potion of giant size
• 3 spell scrolls of shapechange

...and here are our allies:

• 14x Clerics (Grave Domain) 2 ---------------------------------------- for Path to the Grave
• Bard (College of Valor) 18 -------------------------------------------- for Combat Inspiration, the spells wish and simulacrum via Magical Secrets
• Bard (College of Lore) 18/Fighter 2 ---------------------------------- for glyph of warding, the spells banishing smite, branding smite, elemental weapon, flame arrows, simulacrum, spirit shroud, and wish via Magical Secrets, Action Surge, and the Boon of High Magic
• Bard (College of Lore) 18/Fighter 2 ---------------------------------- for glyph of warding, the spells divine favor, enlarge/reduce, haste, holy weapon, simulacrum, Tenser's transformation, and wish via Magical Secrets, Action Surge, and the Boon of High Magic
• Fighter (Eldritch Knight) 17 ------------------------------------------- for Action Surge x2, the wizard spell list, the Metamagic Adept feat, and Combat Inspiration
• Bard (College of Valor) 15 --------------------------------------------- for Combat Inspiration
• Fighter (Eldritch Knight) 17 ------------------------------------------- for Action Surge x2, the wizard spell list, and the Metamagic Adept feat
• Bard (College of Valor) 15 --------------------------------------------- for Combat Inspiration
• Bard (College of Valor) 15/Cleric (Order Domain) 1/Fighter 2 --- for Combat Inspiration, Voice of Authority, and Action Surge
• Bard (College of Valor) 15 --------------------------------------------- for Combat Inspiration
• Fighter (Battle Master) 10/Bard (College of Valor) 10 ------------- for Commander's Strike and Combat Inspiration
• Bard (College of Valor) 15 --------------------------------------------- for Combat Inspiration
• Fighter 6 ----------------------------------------------------------------- for the Squire of Solamnia and Knight of the Crown feats

The Procedure

1. The first Grave Domain cleric uses Path to the Grave on the target.
2. The 13 other Grave Domain cleric Readies Path to the Grave for after our Duergar attacks.
3. Our 18th level Valor Bard gives Bardic Inspiration to our Duergar
4. Our 18th level Valor Bard then casts wish replicating the effects of simulacrum targeting one of the Lore Bards.
5. Each new simulacrum casts wish replicating the effects of glyph of warding to store
6. Each new simulacrum then uses Action Surge to cast wish replicating the effects of simulacrum targeting one of the Lore Bards
7. This is done until we have 35 spell glyphs with the following spells: 14x banishing smites, 14x 8th level branding smites, 7th level elemental weapon, 7th level spirit shroud, divine favor, enlarge, haste, holy weapon, and Tenser's transformation
8. The final simulacrum uses Action Surge to cast flame arrows at 5th level on our Duergar's quiver
9. One of the Lore Bards administers the potion of giant strength to our Duergar
10. Our Duergar uses a spell scroll of shapechange with the Quicken Spell Metamagic to turn into a Marilith and then takes the Attack action three times
11. Both Eldritch Knights use a spell scroll of shapechange with the Quicken Spell Metamagic to turn into either a duergar warlord, or a duergar mind master
12. Both Eldritch Knights then use Call to Attack or Mind Mastery respectively
13. Both Eldritch Knights then use Action Surge to Ready those same actions for the following turns
14. On those proceeding turns, two of our 15th level Valor Bards give Bardic Inspiration to our Duergar before the Eldritch Knight actions
15. Our Order Domain cleric gives Bardic Inspiration to the Duergar and then casts a spell on the Duergar using Voice of Authority
16. Our Order Domain cleric then uses Action Surge to Ready a spell for the purpose of Voice of Authority on the following turn
17. On that proceeding turn, one of our 15th level Valor Bards give Bardic Inspiration to our Duergar before the Order Domain cleric action
18. Our Battle Master gives Bardic Inspiration to our Duergar and then uses Commander's Strike
19. Our final 15th level Valor Bard (who is attuned to a sword of the paruns) gives Bardic Inspiration to our Duergar and then uses the first property of the sword on the Duergar
20. Our Knight of the Crown grants one last attack to our Duergar

The Calculation

Here are the damage elements with all the buffs:

• 2 base attacks from to Tenser's transformation; 2 more attacks from Action Surge; 1 more attack from haste
• 9 reaction attacks from 2x Call to Attack, 2x Mind Mastery, 2x Voice of Authority, Commander's Strike, sword of the paruns, and Knight of the Crown
• Each attack does a base damage of 3d8 + 6d10 + 5 with longbow, arrow of slaying, and potion of giant's strength
• Each attack has the following source of extra damage:
  • branding smite for 5d10
  • 8th level branding smite for 8d6
  • 7th level elemental weapon for 3d4 + 3
  • 7th level spirit shroud for 3d8
  • divine favor for 1d4
  • enlarge for 1d4
  • holy weapon for 2d8
  • Tenser's transformation for 2d12
  • flame arrows for 1d6
  • Major Beneficial artifact properties for 4d6
  • Sharpshooter for 10
• 10 attacks benefit from Sneak Attack for 9d6
• 6 attacks benefit from 15th level Combat Inspiration for 1d12
• 2 attacks benefit from Superiority Dice for 1d6
• 1 attack benefits from the following sources of extra damage:
  • 10th level Combat Inspiration for 1d10
  • Commander's Strike for 1d10
• We reroll one damage die per attack from Piercer
• Every attack is a critical hit from Assassinate (and Piercer grants an extra d8)
• Damage per attack is quadrupled with Path to the Grave and Death Strike
• 14 doses of Purple Worm Poison

Here is the full calculation (dice stacked to take up less space):

$$4*(14*((1*8)+(3*6.5)+(22*5.5)+(17*4.5)+(26*3.5)+(10*2.5)+10+5+3)+10*(18*3.5)+6*(2*6.5)+2*(2*3.5)+1*(4*5.5))+14*(12*3.5) = 23668$$

Note: This relies pretty heavily on turn order. You can force the turns to take a specific order with sufficient quantity of Divination wizards using Portent

Answer 2

Here is what I came up with.

Assume we have surprise first round.

My buffing friends are a lv 20 Lore college Bard, and a Lv 20 Genie Warlock. The bard will be using Glyph of Warding to load the warlocks Genie bottle with the following buffing spells:

• Spirit Shroud lv 9 slot 4d8/att
• Haste: +1 Att
• Swift Quiver: +2 att on bonus action
• Magic Weapon: +3 dam
• Divine Favor: 1d4/Att
• Banishing smite: 5d10
• Branding smite: 9d6

Our sniper will be a Lv4 rogue assassin, lv4 Gloom Stalker Lv12 Fighter Battle master.
Stats: 20 Dex, all other stats meet minimum requirements for multi-class.

Feats: (human 1, ranger 1, rogue 1, fighter 4)

• Sharpshooter: +10 damage
• Martial Adept: (gain one superiority die)
• Piercer: Add 1 damage die on crit, +1 Dex
• Poisoner: ignore resistance to poison
• Dex +2
• Alert: +5 Initiative
• Lucky: re-roll 3/day

Fighting style:

• Archery: +2 to hit
• Fighting Initiate: Gain one superiority die

Total attacks in one round: 11

• Gloom Stalker: +2 attacks, +2d8,
• Assassin: +2d6, all hits are crits
• Fighter: +3 attacks, action surge +3 attacks, Superiority dice:d10s, 5 (total 7)

Total Attacks from classes: 8 Total attacks from spells:3 (Haste, Swift Quiver)

Set up: No Magic Items

Round one, Warlock brings you into his bottle with an action. you use a free action to say the command word and are fully buffed. Warlock then casts you out as a bonus action.

You attack.

11 total attacks, 7 with superiority dice, 2 with dread ambusher dice (ranger) all with sneak attack, all crits.

Attacks: Bow: 1d8(Long bow),1d4(Divine Favor), 4d8(Spirit shroud), 1d8(piercer)

= 6d8+1d4= X 11

77-572 Assuming all hit.

Additional damage:

5d10(Banishing smite), 9d6(Branding Smite), 2d8(Gloomstalker), 7d10(superiority dice) 2d6(sneak attack)

12d10+11d6+2d8=

25-202

Sub total:

102-774

X2 for crit:

204-1548

Plus static damage: +3(Magic), +5(Dex), +10(Sharpshooter) X11 = 198

402-1746

Average Damage: 1074 (no Magic Items)

Notes:

Purple Worm Poison 12d6 (not magical)

414-1818

Avg: 1116 Damage