First,while the 460 Rowland has longer brass,it still has to fit in the 45ACP magazine your pistol was designed for.That is your max LOA limit. For function,its pretty well set in stone.
With some 45 ACP bullet designs,SWC's in particular,Ogive length and SWC shoulder are designed for 45ACP case length /case mouth.If you seat the SWC shoulder as deep as you can in a 460 Rowland case,it won't fit a magazine if the ogive is too long.
I understand you are concerned about the powder volume space under the bullet base,and as you are looking at things,measuring cartridge overall length does not tell you bullet base position. But it certainly can,very easily. Simply measure the length of a bullet. Measure the length of whatever "ideal" bullet is in your loading data that gives you a cartridge LOA. Subtract.The cartridge Length overall minus the bullet length will give you a case head to bullet base measurement.
So,indirectly,you can measure and compare bullet base position via cartridge overall length.
That gives you the answer to your pressure question.
I'm not sure I understand the relevance of the ogive comparator.Isn't that generally about controlling centerfire rifle bullet distance from the rifling lands?
If I understand,the comparator is a way to find an answer to a different question.
Are you concerned about bullet to bullet manufacturing variation?.Probably close enough.Every bullet in the box probably came out of the same die.
If your seater punch is not finding a consistent surface on the bullet to reference,maybe a change in seater punch is in order. A seater punch and a bullet comparator or calipers both reference a surface on the bullet .
How you balance acceptable magazine and feed length against bullet base/COAL/powder volume is one of the joys of owning a 460 Rowland.
Most bullets are designed to suit the 45ACP case length.Using a longer 460 Rowland case in the same magazine length makes a number of 45 ACP bullet designs unusable in a 460 Rowland
