In the runes there is crit damage runes and I wanna know how i could make myself do the most damage with 1 auto assuming it crits(wont need crit chance in runes because of the scaling AD vs Critical strike damage
rampaging poet1 votesAssuming you crit, each point of % critical damage adds 1% of your AD to your damage. When you critically strike, critical damage marks break even with flat attack damage marks at 42.6 AD and with scaling AD marks at 109 AD. Critical damage quintessences break even with flat AD quints at 50.4 AD and with scaling quints at 101 AD. When your champion has at least that much AD without runes their critical strikes will deal more damage if they have critical strike damage runes than if they had AD runes.
However, in practice critical damage runes are weaker than AD runes (or even armour penetration) for two reasons: you need a high critical chance to make them effective and they are useless against structures. The actual amount of damage you can expect to gain from a critical damage rune is (Current AD) * (Crit % Chance) * (Crit Damage % Bonus) / 10000. This is because it adds a small percent of your AD, but only a small percent of the time.
Critical Damage runes are useless early game because you won't have enough critical hit chance for them to pay off AND it's cheaper to invest in more attack damage early on. They can be useful as a late-game scaling tactic on ADCs because most ADCs reach over 200 AD and about 50% critical hit chance from their build. The problem is that they don't help you win until you have your first item or two, so it's possible for someone with better early-game runes to force you out of lane enough that you can't get the items you need for your runes to work.
Byakuya Kuchiki1 votes[{quoted}](name=rampaging poet,realm=NA,application-id=WEuoGbmp,discussion-id=fI9b8qJw,comment-id=0000,timestamp=2015-06-21T08:31:36.395+0000)
Assuming you crit, each point of % critical damage adds 1% of your AD to your damage. When you critically strike, critical damage marks break even with flat attack damage marks at 42.6 AD and with scaling AD marks at 109 AD. Critical damage quintessences break even with flat AD quints at 50.4 AD and with scaling quints at 101 AD. When your champion has at least that much AD without runes their critical strikes will deal more damage if they have critical strike damage runes than if they had AD runes.
However, in practice critical damage runes are weaker than AD runes (or even armour penetration) for two reasons: you need a high critical chance to make them effective and they are useless against structures. The actual amount of damage you can expect to gain from a critical damage rune is (Current AD) * (Crit % Chance) * (Crit Damage % Bonus) / 10000. This is because it adds a small percent of your AD, but only a small percent of the time.
Critical Damage runes are useless early game because you won't have enough critical hit chance for them to pay off AND it's cheaper to invest in more attack damage early on. They can be useful as a late-game scaling tactic on ADCs because most ADCs reach over 200 AD and about 50% critical hit chance from their build. The problem is that they don't help you win until you have your first item or two, so it's possible for someone with better early-game runes to force you out of lane enough that you can't get the items you need for your runes to work.
lets say i built 5 
and a full stacked
and all the masteries that make my autos do more damage and give me more AD, i would do more damage with a full set of crit damage runes than a full set of scaling AD correct? im not gonna try this im just wondering in theory
rampaging poet1 votesThat is way, way, way overkill for just "crit damage being better." The fully-stacked Sword of the Occult alone gives enough AD for crit damage marks to deal more damage on crit than scaling AD marks. That build hits 100% crit chance and has 520 bonus AD, so you will crit (essentially) every attack for somewhere in the neighbourhood of 1600 damage.
From the Wiki, Shaco gets some bonus crit damage with Deceive at max rank, and more for backstabbing. He's probably your go-to champion for trying to crit for as much pre-armour damage as possible in a single attack.
I strongly advise not doing this in a real game because you are missing a lot of other important stats. You have no boots, so you can't catch anyone or run away if things go sideways. You have no defences, so you die instantly to anyone else with burst damage. You have no lifesteal, so any damage you take from poke will stick. You have no armour penetration, so people stacking armour severely reduce the damage they actually take. If the enemy buys Thornmail, you will have a very, very bad time.
Also, that build costs about 20,000 gp. Hope you like hour-long games!
ZACKandATTACK1 votescrit damage runes are never worth it