I am new to the world of neck turning brass. So I am looking through the Midway catalog and see only I think it was two manufacturers of neck turning equipment for the 50 BMG cartridge. And i clearly remember one you have to buy separate pilots for the tool. There were two possible offerings, one in .510" and one for .513". I suppose one .513 would be used before sizing, but not sure of the .510".
If the brass after sizing would have an inside neck dia smaller so that it can hold a .510 bullet, Then shouldn't be to small for a .510 pilot.

Please teach me up on neck sizing. I am a total noob to neck sizing other than the reason to do so

The Forster one works fine.  Can be use for all cases up to the .50.  Get the .510 pilot.  Always turn after sizing.

The Forster .510 pilot is well under .510 O.D., its made to be used after sizing the case.

I can measure it tomorrow if you really need to know what it is.

thanks guys for your input. yes I do plan to join shortly. Well I had a senior moment. I went back into my Midway catalog and found that the pilot is .002 to .0025 undersized from the stated pilot size that they sell. So the .510 is actually .508 or .5075. So, yes after sizing the shell I should have a tight fit to the pilot.

Again thanks guys this answered my question. I just could not see how a pilot that is the same size as the bullet, that is suppose to be tight in the neck. Then how could the pilot allow the brass to be turned on the pilot?  I would have thought that the pilot would be tough enough to get it in the neck. Once I read that the pilot was undersized, then it all made sense.