I am not USBP but met a few of their team members past an present. So here is what I have gleaned: First here is a link:https://www.ssusa.org/articles/2015/12/7/interview-with-2015-npsc-champion-robert-vadasz/
You can search for more. Most of the top guys shoot 1911s or S&W PPC9s for Open and distinguished. I have seen a lot of Springfield 1911s for Service semi and some S&W 952s. Springfield Ultras are popular for off duty. All in 9 mm. Not sure about service revolvers probably a mix of K and L frame S&Ws. Distinguished revolvers tend to be Model 14s with some 586s or 686s. Open Revolvers are from all the good custom shops Mojo and others. Hope this helps.