User blog:Geomax/Perfectly Reasonable 40k Firepower Calcs

I see on the Adeptus Astartes page that Bolter firepower is said to be just Large Building level. I am about to show that this is a severe underestimation.

First off, Bolter rounds used against humans tend to be pretty consistent in destroying large amounts of their bodies:
 * The bolt pistols thundered again. Each round found its mark, and fifty more bodies were reduced to bloody fragments. The rest of the mob staggered on, their outstretched hands little more than a metre away.
 * At Zahariel’s command, the squad took one last step back and fired five more rounds into the press. Firing bolts locked back on empty magazines as fifty more bodies erupted into gory mist. The mob had been cut in half in the span of twenty seconds, but the remainder pressed their advance.
 * - Fallen Angels
 * ‘Stupid,’ said Ghota, drawing his heavy pistol with such swiftness that Palladis wasn’t sure what he’d seen until the deafening bang filled the chamber with noise. Everyone screamed, and went on screaming as they saw what the gunshot had done to Estaben.
 * It had destroyed him. Literally destroyed him.
 * The impact pulped his upper body, hurling it across the chamber and breaking it apart over the chest of the Vacant Angel. Ribbons of shredded meat drooled from the statue’s praying hands and sticky brain matter and fragments of skull decorated its featureless face.
 * - The Outcast Dead
 * Natraj was dead before Tirtha hit the ground. Uttam’s guardian spear spat a bolt from the weapon beneath the blade and the man’s body blew apart into vaporised blood and bone shrapnel. Two of the nearest soldiers went down with the force of the explosion, but Uttam was already moving as alarm klaxons and warning bells filled the cavern with noise.
 * - The Outcast Dead
 * He swung his bolter up. His weapon had a gash in the metal of the foregrip, the legacy of a greenskin’s axe during Ullanor, a cosmetic mark Loken had told the armourers not to finish out. He began to fire, not on burst, but on single shot, feeling the weapon buck and kick against his palms. Bolter rounds were explosive penetrators. The men he hit popped like blisters, or shredded like bursting fruit. Pink mist fumed off every ruptured figure as it fell.
 * - Horus Rising
 * Now, these effects might only seem to be roughly around the same level as modern day 20-30mm autocannon rounds in terms of firepower. However, this assumes that 40k humans take the same amount of energy to destroy as real humans, which seems to be very much mistaken:
 * A fist of gaseous matter as hot as the core of a star ripped into the shadow’s left arm, just above the elbow. Everything below the joint exploded from the touch of the incredible heat, and the hydrostatic shock of boiling blood sent a hammer blow racing through the killer’s body. The assassin tumbled from the bookcases, falling to the decks through wreaths of fire-retardant mist.
 * Plasma weapons were designed not to target un-armoured forms like the shadow, but to melt their way through ceramite or hull metal. Used on flesh, they were a blowtorch turned upon wax. The pain of the hit was of such intensity that the killer’s heart was stopped by it, and in turn, this factor triggered the compact denial charge of hexogen that was implanted beneath the shadow’s ribcage. The assassin’s patron was not in the business of letting discarded tools fall into the wrong hands.
 * With a wet crack, the shadow blew apart in mid-air.
 * Source: Faith & Fire - Chapter Eight
 * As Matthew Schroeder previously calced, "hot as the core of a star" show the plasma built to deliver around 1.4 gigatons of energy on the low end. Since there is clearly no way this calc could possibly been mistaken, and given that only her joint was actually destroyed by the hit, this clearly shows 40k humans can take gigaton firepower from anywhere beyond a quarter meter or so. Given that bolters are displayed destroying 40k human torsos with single shots this suggests firepower on a comparable order.
 * A fist of gaseous matter as hot as the core of a star ripped into the shadow’s left arm, just above the elbow. Everything below the joint exploded from the touch of the incredible heat, and the hydrostatic shock of boiling blood sent a hammer blow racing through the killer’s body. The assassin tumbled from the bookcases, falling to the decks through wreaths of fire-retardant mist.
 * Plasma weapons were designed not to target un-armoured forms like the shadow, but to melt their way through ceramite or hull metal. Used on flesh, they were a blowtorch turned upon wax. The pain of the hit was of such intensity that the killer’s heart was stopped by it, and in turn, this factor triggered the compact denial charge of hexogen that was implanted beneath the shadow’s ribcage. The assassin’s patron was not in the business of letting discarded tools fall into the wrong hands.
 * With a wet crack, the shadow blew apart in mid-air.
 * Source: Faith & Fire - Chapter Eight
 * As Matthew Schroeder previously calced, "hot as the core of a star" show the plasma built to deliver around 1.4 gigatons of energy on the low end. Since there is clearly no way this calc could possibly been mistaken, and given that only her joint was actually destroyed by the hit, this clearly shows 40k humans can take gigaton firepower from anywhere beyond a quarter meter or so. Given that bolters are displayed destroying 40k human torsos with single shots this suggests firepower on a comparable order.
 * As Matthew Schroeder previously calced, "hot as the core of a star" show the plasma built to deliver around 1.4 gigatons of energy on the low end. Since there is clearly no way this calc could possibly been mistaken, and given that only her joint was actually destroyed by the hit, this clearly shows 40k humans can take gigaton firepower from anywhere beyond a quarter meter or so. Given that bolters are displayed destroying 40k human torsos with single shots this suggests firepower on a comparable order.

Now, we can also use this to get firepower for larger 40k weapons. Assuming a yield of 1.4 gigatons for a bolter shell, assuming that it weighs around the same as a round from a 20mm M61 Vulcan (i.e. 0.1 kg), assuming that a Battle cannon shell weighs the same as an M830 120mm HEAT shell (i.e. 24.2 kg) and assuming a comparable percentage of mass filling with a comparable yield explosive, this gives a yield of 338.8 gigatons for the main gun of a Leman Russ MBT. This will clearly be necessary for destroying 40k steel, which can also take gigaton firepower at point blank.

''Miriya fired, releasing a salvo of quick energy bolts up into the steel rafters. She could not see the attacker, but the Celestian’s mind operated on an instinctual, instantaneous level. There was some part of her consciousness calculating angles and likely points of attack, aiming at the places where she herself might have hidden in order to kill the girl. And there! For a fraction of a second, backlit by a streak of sun-bright gaseous plasma, a man-shape recoiling in the girders.''

Source: Faith & Fire - Chapter Eight

Now, lets move up to starships.

''Mars Pattern Macrocannons

The most common macrobattery, these are reliable, hard-hitting weapons firing kilo-tonne ordinance, mounted along the vessel's dorsal ridge or in broadside.

Mars Pattern Macrocannon Broadside

The most common macrobattery, these are reliable, hard-hitting weapons firing kilo-tonne ordinance, mounted along the vessel's dorsal ridge or in broadside. Broadside: These weapons must occupy a Port or Starboard Weapon Capacity slot. -Rogue Trader Core Rulebook, Page 202''

Going low end and assuming a mass of 1000 tons, while assuming a comparable explosive type and filling percentage to Bolters, this gives a yield of 14 petatons for a single Macrocannon round, ignoring the round kinetic energy. This level of firepower show how 40k ships are able to destroy the surfaces of 40k planets, on which the atmosphere's specific heat capacity is large enough for gigaton level blasts to not generate huge explosions.