Yes, a hole saw can wobble and make hole slightly larger. To minimize this, as soon as pilot hole is through replace the drill bit with a smooth rod (mine was 1/4”). Run the hole saw SLOWLY with a little cutting oil.
I disassembled my cold air induction system to get my information right. My hole, using a 4.125 saw measured 4.149”, just .024” larger.
The groove in my ‘donut’ measures 3.935” or about .2” (3/16”) smaller than the recommended 4.125”. Even a 4” hole would be slightly large. Will post a couple pictures as soon as I can get them to download from my phone. As said before, DO NOT make your hole before checking.
Yote