What, exactly, is "pistol ammo"?
.223 or .308 for an AR pistol?
410 for a Judge?
.45LC or .38/.357 or .44 for a lever-action rifle?
.22LR for a 10/22 rifle?
30/30 for a BFR?
If there's a legal definition of "pistol ammo", would that not imply a corresponding legal definition of "pistol", based...
Sounds like dealers being bitches. "the ATF agent said ..." is a good excuse.
Take your business - ALL purchases - elsewhere.
And let others know who to avoid.
Given that logic, using a 30/30 lever gun would get you in more trouble too.
How many professional instructors and coaches, cops, prison guards, and private security teams use them?