Here we go with this again....

What is so special about the 'first yard' that the load would lose over 100 fps?

Drag does indeed vary as the square of the velocity, but that applies to each and every yard.

There is such a thing as trans sonic drag variation, but that's velocity related and has nothing to do with position relative to the muzzle. In fact, we launch pellets over quite a range relative to sonic, which is 'roughly' 1125 fps (it varies with temperature).

I call BS on the 'rapid loss of velocity in the first yard'.

"The price of good shotgunnery is constant practice" - Fred Kimble