You are sorta on the right track but there are some caveats to that. A tighter chamber with a short throat will also generate a lot of pressure with a smaller charge. For instance I have a 338RUM which I had built off a 338 win mag action. The mag was plenty long but not as long as it could have been to allow me to seat a bullet out very far. So I had the gunsmith throat the chamber to allow me to still seat close to the lands and fit the mag which seats the bullet well into the case
Bear with me on this.
This means the size of the combustion chamber (total volume of the chamber) is smaller than a normally sized 338RUM chamber which is known to have a long throat. In all of the RUM's that I have heard about you can not load close to the lands. In mine since I have a smaller combustion chamber I do not have to load as much powder to achieve the same velocity and can not load up to book max. For instance the book max load for RL25 with 225 gr bullets is 98 grains. I get small pressure signs like slight extractor groove marks at 96 gr RL25 and I can load 94 gr RL25 and get the velocity shown for the max load in the book for 98 gr RL25.
So I have a tight chamber including a short throat and can get velocity.
But you are right in that if you have a long throat you can load more slow powder than I could because you would have a larger combustion chamber. It is what Weatherby has used for years to put hot loads in their Wtby calibers. If you were to get a custom chamber in a Wtby caliber then you would not want to get a short throat and shoot factory ammo!!!! NO NO. Could produce enough pressure to blow the gun up.
I will not ever shoot factory ammo in this 338RUM even though it might be possible if the factory loads were a little anemic. Wtby factory loads are loaded HOT to get all that velocity they tout.
What was the question?
"will seating the bullet as long as possible allow for greater FPS and still acceptable pressure by increasing the potential powder charge? There for use a heavier load of slower powder like H1000 insted of H4831SC."
put it this way: you will NEED to use more powder to generate the SAME fps as you would have been able to achieve with a shorter throat and less powder.
"Some day I will build a long range 300 win mag. Of course looking at heavy pills (190,208,210 etc.) at max FPS. Lets say I seat the bullet at or in the lands, the variable becomes the OAL in reguards to the length of throat correct? A long throat on this caliber will allow room for more powder, am I on track so far? So a long barrel of 28-30" sould be able to take advantage of the extra powder and generate more FPS as compared to seating the bullet at the standard 3.34" in a standard chamber yet still in the lands?"
IMO, the best way to do it is to have the shortest throat that will also allow anyone to shoot factory ammo. The 300 win mag has plenty of case capacity to get enough powder in the case and you can gain velocity easier by loading close to the lands and having a small combustion chamber.
An exception to this would be if you were getting a custom chamber in a caliber that did not have enough case capacity or the case capacity would be reduced by seating a bullet down in the case. For instance I have a custom 6.5 rem mag that I rebarreled off a 300 win mag (long throat short mag Browning BBR) and I had the gunsmith set the lands so I could load those long 6.5 bullets way out there in order to stay out of the powder capacity
Perhaps nhenhinge can come up with a short catchy analogy!!