if i use war caster opportunity attack can i use a spell for a action

Me and my father seem to have a disagreement regarding the feat war cast which says  "When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature"  he says if I use this to do a spell as a reaction I can't cast a spell during my turn is this true

Under 5.5e rules, you can cast only one spell with a spell slot on your turn. However, by definition, a reaction does NOT happen on your turn; it happens on someone else's turn.  EDIT: All right, technically, there are SOME features which allow you to use a reaction on your own turn. However, they're not relevant to the question. The trigger for the reaction Warcaster uses can only happen on a hostile creature's turn. Therefore, you can indeed cast a spell on your turn and also use Warcaster to cast a spell (which meets the requirements stipulated by Warcaster) as a Reaction .

Quote from Stabbey_TC >>

Under 5.5e rules, you can cast only one spell with a spell slot on your turn. However, by definition, a reaction does NOT happen on your turn; it happens on someone else's turn. Therefore, you can indeed cast a spell on your turn and also use Warcaster to cast a spell (which meets the requirements stipulated by Warcaster) as a Reaction .

The second sentence is not true. It's true that reactions are almost always taken on another creature's turn, but there is no restriction that they must. Counterspelling a counterspell is one of the great examples of using your reaction on your own turn.

As for the OP, though... if you are using your reaction as an OA to then turn into a spell, you are indeed taking that on another creature's turn and will be able to cast a spell with a spell slot when it's your turn as well.

Dad is wrong.

If you use warcaster feat to cast a spell as an opportunity attack, that means someone left your reach, which likely happened because they moved away from you during their turn. You can only burn one spell slot per turn, so if they moved away from you on THEIR turn, you could burn a slot on their turn for the OA. Then on YOUR turn, you could burn a slot for something else.

Note: it is possible that on YOUR turn, you burn a slot to cast Dissonant Whispers, which causes the target to use their reaction to run away ON YOUR TURN.  This means your opportunity attack using warcaster would have to use a cantrip or some non-slotted spell

Quote from sabin76 >>

Counterspelling a counterspell is one of the great examples of using your reaction on your own turn.

This is also much less likely due to 2024 rules. If you cast fireball with a slot and en enemy counterspells it, you cant cast counterspell because you already used a slot to cast fireball and you cant burn 2 slots innthe same turn.

Quote from SunIsGettingRealLow96589 >>

Quote from sabin76 >>

Counterspelling a counterspell is one of the great examples of using your reaction on your own turn.

 

This is also much less likely due to 2024 rules. If you cast fireball with a slot and en enemy counterspells it, you cant cast counterspell because you already used a slot to cast fireball and you cant burn 2 slots innthe same turn.

I agree. It's possible to do with an initial casting of a cantrip, but at that point, I'd just let the CS go through. Wasting a CS on a cantrip is very much in the cantrip caster's favor the vast majority of the time.

Quote from Angel_of_death11 >>

he says if I use this to do a spell as a reaction I can't cast a spell during my turn is this true 

99% of the time this is not true, because you'll typically be using this to cast a spell using your reaction outside of your turn and that won't affect what you can cast during your following or preceeding turn.

The 1% exception would be if the creature is somehow provoking an opportunity attack on your turn, and even then it'd depend on which rules version (5e or 5.5e) you're using and which spells you've used or want to use.

For example, under 5e rules you cannot cast a bonus action spell in the same turn as any other spell except a cantrip of casting time of 1 action. This means if you have already cast a bonus action spell, you can't cast a spell as a reaction. And if you cast a spell as a reaction, you can't then cast a spell as a bonus action (but you could cast a spell as an action, confusing I know)

Under 5.5e rules, it's much simpler—you cannot spend more than 1 spell slot to cast spells in a given turn. So if you use your reaction to cast a spell using a spell slot, you can't spend another spell slot on a spell for that turn. And if you've already spent a spell slot on a spell that turn, you can't use your reaction to spend a second spell slot.

But again, that's like an edge case. In the general case, your dad is incorrect

Quote from Deyric >>

Quote from Angel_of_death11 >>

Me and my father seem to have a disagreement regarding the feat war cast which says  "When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature"  he says if I use this to do a spell as a reaction I can't cast a spell during my turn is this true

 

 Sage Advice disagrees with your father. 

Reaction attacks from War Caster do not take away your next rounds action. 

 5e Sage Advice, or 5.5e Sage Advice?

Deyric, you seem to be referring to 5e rather than 5.5e. For example, you cannot Counterspell someone who Counterspelled your own spell anymore due to the new rules on spellcasting which prevents more than one spell slot being spent in a turn, contrary to the example you gave in post #11. While it's not explicitly stated in the original post, we should assume that someone is using the most current form of the rules - which is 5.5e and what people in subsequent posts are referring to. 

They are correct in what they've said.

Quote from Deyric >>

 

Quote from SunIsGettingRealLow96589 >>

Quote from sabin76 >>

Counterspelling a counterspell is one of the great examples of using your reaction on your own turn.

 

This is also much less likely due to 2024 rules. If you cast fireball with a slot and en enemy counterspells it, you cant cast counterspell because you already used a slot to cast fireball and you cant burn 2 slots innthe same turn.

 Absolutely false according to Sage advice. 

"Can you cast a reaction spell on your turn?

"You sure can! Here’s a common way for it to happen: Cornelius the wizard is casting fireball on his turn, and his foe casts counterspell on him. Cornelius also has counterspell prepared, so he uses his reaction to cast it and break his foe’s counterspell before it can stop fireball."

It literally tackles your exact scenario.  Reactions are exceptions to the limit, but have to be a reaction spell.  

 You're quoting the wrong Sage Advice—that's the 2014 SAC and you're using it in response to someone very explicitly referencing the 2024 rules (highlighted). Here's the 2024 SAC on the same question:

Can you cast a Reaction spell on your turn?
Yes, but you must abide by the rule of expending only one spell slot to cast a spell on your turn. For example, if you take a Magic action to cast Fireball using a spell slot and an enemy casts Counterspell, you can’t also then expend a spell slot to cast Counterspell targeting that enemy.

In fact, the 2014 and 2024 SACs for the exact same questions give completely opposite examples due to how the rules changed between 5e and 5.5e

Quote from Deyric>>

Quote from Davyd>>

Quote from Angel_of_death11>>

he says if I use this to do a spell as a reaction I can't cast a spell during my turn is this true 

But again, that's like an edge case. In the general case, your dad is incorrect

 Sage Advice disagrees with his father and you. 

And by your ruling, reaction spells would take away spellcasting for your next round as well.  They don't. You can cast a spell your turn, and cast Shield as a reaction, or Counter Spell as a reaction.  And you can still cast on your next turn after using them.

No? I never said that, I said the literal opposite. I am honestly quite stunned that you could read the words I typed and then come to the conclusion that's what I'm saying.

I'll try rephrasing it:

There is a very specific edge case that could result in Warcaster preventing you from casting further spells. Otherwise it doesn't impose any such limit

2014 Rules:

Casting a spell using Warcaster would only restrict your ability to cast a spell if all of the following are true:

1. An enemy moves on your turn
2. This movement provokes an opportunity attack
3. You use your reaction as part of that opportunity attack to cast a spell
4. You then later in that turn want to cast a Bonus Action spell specifically

You would not be able to cast that Bonus Action spell due to the BA spellcasting rule. However, you would not be restricted from casting spells with any other casting time during that same turn of yours.

Additionally, if on that turn before the opportunity attack you had cast a Bonus Action spell, you would not be able to perform step 3 of the above. Again due to the same BA spellcasting rule.

2024 Rules:

1. An enemy moves on your turn
2. This movement provokes an opportunity attack
3. You use your reaction as part of that opportunity attack to cast a spell using a spell slot
4. You then later that turn want to cast another spell using a spell slot

You would not be able to use a spell slot to cast a spell later in that turn due to the 2024 two spell slot rule. However, you can cast cantrips and you can also use spell slots for other game features.

Likewise, if you'd already used a spell slot prior to step 3, you wouldn't be able to. However you could instead use a cantrip at step 3

Again, to reitterate, these are edge cases and normally warcaster (and reaction spellcasting in general) does not impact your ability to cast spells on subsequent turns. 

Judging by the legacy version of War Caster quoted, The OP isn't playing 5.5E. 

Quote from Angel_of_death11 >>

Me and my father seem to have a disagreement regarding the feat war cast which says  "When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature"  he says if I use this to do a spell as a reaction I can't cast a spell during my turn is this true

 No it's not true, using War Caster Reaction has no impact on your next turn's action.

If on your turn you use your reaction to cast a spell with War Caster, the only imitation would be if you also cast a spell as a bonus action. 

You can't cast another spell during the same turn, except for a cantrip with a casting time of 1 action.