First of all I want to say that I love Underwood Ammo. Underwood is showing the industry how it's supposed to be done! And I carry Underwood 45 Super or 10mm daily.
That being said, I still have 95% of a box of Underwood 40S&W 135gr @1500fps. I tried to shoot them out of a Sig 250C and my Glock 29 and both could not fire them, I'm assuming hard primers. I did, very briefly, have a Ruger SR40C that I seem to remember (I got CRS) fired those rounds without a problem.