Probably actually a 3.5"
My ACT mags are OK range magazines, I picked up Wilson for social work.
Be aware that Armscor's compact design is reliable - at the cost of reduced recoil spring life. If you're a high-volume shooter, get in touch with Armscor (Nevada) or Wolff and have a spare on hand. They're under $10, or they were when I ordered three along with other stuff from Armscor.