how do you determine the correct bullet seat depth ,I am loading 223 hornaday 50g v max and sierra 55g spitzer with hogdon h335 starting with a lite load (24g)and understand that the max coal for 223 is 2.260 and that is so they will fit into the magazine I need to know how to find the data for bullet seat depth and corresponding coal based on the bullet and powder selection any help would be appreciated

Easy answer; for autos; make the rounds fit your magazine. Period. For bolt actions, you want to play with oal and distance to rifling, but for autos, you are limited to mag length. You can only alter that to some degree; go by the book length first. Closer to the rifling without touching is a good place to start. this topic has been discussed much, here on AR.

Unless you are shooting one at a time loading through the port by hand you are limited by your magazine length on bolt guns also

the bullet mfr will tell you the COAL for that bullet.

Put a bullet against the throat/rifeling, take a cleaning rod in the mussle to the bullet put a mark mark a how long it were. take the bullet out messure with the cleaning rod to the bolt head. The distance between the mark -1mm is your max oal with that bullet. Make sure it fits magazine and the bullet is at least one diameter(or 80%) inside the caseneck.

Ok, back to the one bullet diameter of seating; that is impossible on many rounds, including the .223 and others. Ignore that "rule" and seat for accuracy, and mag function. Nordic is right on how to find your max OAL. Adjust from there. Bolt guns usually have longer mags, I have found, than AR-15 mags so you can get your bullets closer to the throat. Depending on your rifle.

Look in your loading manual. The info is there. You are using one, aren't you? It'll tell you the OAL.
Bear in Fairbanks