Do-nuts occur at the junction of the neck/shoulder and are caused by brass flowing along the shoulder and causing a ridge that won't let the bullet pass by in a fired unsized case
the only way to get rid of them is with an inside neck reamer. But they only occur in a tight necked custom reamed chamber.
The way you tell is to take a bullet and try to insert into a fired unsized case and if it hits an obstruction at the neck/shoulder then you have a problem. Essentially they act like a rear crimp.
I wouldn't say you can do load development for the first firing of a 280 rem case. The internal capacity is different enough to cause differences in the subsequent loads. However you could just use them for hunting or trigger time.
My 280AI is my pivot gun in that I take it hunting whether Elk, Antelope or Whitetail along with another gun more appropriate to the game. For example going Elk hunting I will take the 280AI and a 338RUM or for Whitetail the 280AI and my 6.5 rem mag will go. IOW I feel confident it will get the job done from small game to Elk with the 160 gr Accubond at 3000 fps.
Personally I don't like a short action because of possible feeding problems and less magazine capacity. My 280AI will hold 6 down in the mag and feeds slick. I have seen problems with the Wissum's in those short actions and then have seen others that will feed just fine. Even if you don't have feeding problems you will probably have the problem of a longer bullet having to be seated so deep it intrudes on powder capacity. I have dies for and have reloaded for 270 WSM and 300 WSM
's and personally will probably never own one.
Besides, there is still a lot of class to walk into deer camp with a 280 Ackley, IMO