A look at the ULTRA series
The NERF community first got wind of the ULTRA series when a listing of the ULTRA ONE and dart refill pack was leaked in early 2019. Later, in September 2019, an image of the ULTRA ONE blaster was leaked, and on the 1st of October, NERF officially launched the ULTRA series.
The ULTRA series is based around it's new proprietary ammunition. The ULTRA DART is a aerodynamic dart made of a kind of Styrofoam-like substance. It is brittle and not as flexible as most foam darts, and is damaged much easier. The ULTRA DART features built-in fins, a streamlined head, similar to that of the Mega Dart, and a "nub" on the back end that is necessary to make the dart work in the blaster... So the bottom line is that the ULTRA series is NOT compatible with any other blaster series.