Twice during my home campaign session, the question came up: If you hit or miss with an at-will attack power that uses a standard action, can you use an action point to try the attack again?
There is no published RAW deal (Rules As Written) to answer this question, so let's start by looking at some examples of power limits.
The wizard powers: Magic Missile and Wizard’s Fury.
Magic Missile is a Level 1 at-will power that normally requires a standard action to execute.
The daily power Wizard's Fury (also level 1) has the following effect: "Until the end of the encounter, as a minor action once per turn, you can cast magic missile."
This is an example of the limit of once per turn for a power. It does not allow the magic missile to be cast as standard action and a minor action in the same round. This is because by executing Wizard's Fury, the player has changed the action type for Magic Missile from a standard action to a minor action, with the once per turn restriction built in.
The Opportunity Attack.
An opportunity attack is a melee basic attack that is triggered usually in one of three ways: the target leaves your threatened square, the target makes a ranged attack while adjacent to you, or the target makes an area attack while adjacent to you. An opportunity attack is a free action that acts as an immediate interrupt, which interrupts the target's action long enough to execute the opportunity attack, after which the target continues with its action if it can. So it won't halt movement or stop an attack. Here is the key component of the opportunity attack: "You can take only one opportunity action during another combatants turn, but you can take any number during a round.” This RAW deal allows for multiple melee basic attacks per round, but only against different monsters. This is why if three kobolds run past you, you get to make an opportunity attack against each one, but only one attack per kobold. It is also why if during its move a kobold leaves your threatened square, enters another of your threatened squares, then leaves that second square, the kobold does not receive two attacks of opportunity from you.
I’d like to also clarify that if all the kobolds act on the same initiative count, it does not imply that they all act as a unit or should be considered as anything other than individual monsters. Grouping monsters by type into the initiative queue is an act of convenience only for a DM to run the game. Each monster is considered to have its own initiative and its own turn with its own set of actions, regardless of its actual place in the initiative order or whether all the kobold pikemen act on initiative count 18.
The Free Action.
There is a "seemingly" conflicting RAW deal to the opportunity attack, which occurs under the rules of attacking using a free action. An opportunity attack occurs as a free action, but triggered attack powers are also executed as a free action (or sometimes no action). The RAW deal states: "A creature can take a free action to use an attack power only once per turn.” The idea behind it is to prevent a player who has two triggered powers from using both powers if both triggers occur. That means if I have an attack power that triggers when a creature uses a charm spell, and another that occurs if the creature shifts away from me, I can only use one of those triggered powers if the spell both is a charm and allows the creature to shift.
Note that this free action rule is specifically "once per turn", and the triggered attack would occur on the monster's turn (the trigger's turn). So, you can still only make one opportunity attack as a free action on a monster's turn, but you can make another opportunity attack as a free action on the next monster's turn, should the attack be triggered, thus allowing you to make multiple opportunity attacks in a round. So although this RAW deal looks like it confuses the issue, the "once per round" vs. "once per turn" ends up clarifying the deal, oddly enough.
Turn vs. Round
To clarify, each player character and each monster gets its own turn, which comprises three parts: The start of the turn (where it takes ongoing damage but can take no actions), the middle of the turn (where it takes actions), and the end of its turn (where it makes saving throws and can take no actions). The collection of turns for all creatures, traps, etc., constitutes the round. Or the time from the start of your turn to the start of your next turn represents one round. In combat interpretations, all creatures are thought to act simultaneously, where one round represents about 6 seconds of combat. With each turn occurring at the same time, each turn also represents about 6 seconds of combat. But this is only for understanding the role of combat for D&D, and needs to be kept completely separate from the adjudication of combat rules, initiative, turns, and rounds.
The Witch Bolt.
The witch bolt is a Level 1 wizard at-will attack. It uses a standard action to execute. However, it has a "Sustain Standard: Reroll the damage and deal it to the target again.” So here is the question: After using this power, can a player use an action point and use the 'sustain standard' to deal damage again?
What would you say?
My answer: No. Here's why: The RAW deal for sustaining powers is this: "An effect that has a 'sustain standard', a 'sustain move', or a 'sustain minor' duration lasts as long as you sustain it. Starting on the turn after you create an effect, you sustain the effect by taking the indicated action.” The second sentence answers the question clearly. You cannot sustain the power until the turn after you execute the power. Thus, it prevents the power from being used twice in the same turn.
This is a warlock utility at-will power that can be used as a free action. It has a trigger of killing a creature, which then allows the 'effect' of gaining a bonus to attack rolls. However, it has a "special" entry that states "you can use this power only once per round.” So this is one of dozens of examples of powers with usage restrictions of once per round, especially when the action type is move, minor, or free.
Let's look at another Warlock power. Darkspiral Aura is an immediate interrupt power (which would occur on a monster's turn and therefore occurs as a free action for the player). Originally, the trigger stated "Once per round as a free action when an enemy makes a melee attack or a ranged attack against you, you can use your Darkspiral Aura as an immediate interrupt." But in 2009, the published errata rewrote this as "When an enemy makes a melee attack or a ranged attack against you, you can use your Darkspiral Aura as an immediate interrupt."
Why the change in wording? Because the power could be used more than "once per round" if more than one monster triggered it. But, under the RAW deal for attacking as a Free Action, you cannot make more than one triggered attack against a single monster in a round. The power still can only be used once against a given target in a given round.
To sum up:
There are no RAW deals that specifically prevent the use of an at-will attack power as standard action more than once in a round. I think this is mainly because there is normally only one standard action available in a round. The only exception to this is when using an action point to take an extra action (which could be either a standard, move, or minor action). But there is ample evidence of restricting attack powers to once per round or once per turn. Durations of effects and circular loops across powers (where one power triggers another power, which triggers the first power again) have been 'fixed' extensively in the published errata. I think nearly exclusively, no attack power that takes only a move, minor, or free action to execute can be used more than once in a round. (I’m sure there are exceptions.) As a role playing device, I think the magic or gumption used by a player to execute an attack power uses up that magic or gumption, whether they hit or miss, and prevents the power from being used again until the player's next turn. You can use a basic attack more than once in a round, but only once per turn. And I think this gives us a fundamental ruling that we can rely on.
Using the idea of specific beats general: Unless specified otherwise, an attack power can be used more than once per round, but only once per turn. This seems like a reasonable ruling where there is no RAW deal from Wizards. Thus, here is my answer to the question: If you hit or miss with an at-will attack power that uses a standard action, can you use an action point to try the attack again? No, unless the power specifies otherwise.