Oil Pressure gauge freaking out

So I have a mechanical Autometer gauge and on start up I get 70psi on my new engine, but when it starts to warm up the gauge will flutter between 60-70 and then 40-60 when fully warm. I am trying to figure out if this gauge is crap or if I have a bigger issue. I wish I could upload a video, but IDK if it will let me up load a video as I would a picture.

Also when I mean fluttering... I mean 40-60 constantly, not slowly just back and fourth.