Read the Fortune City US Fed Agency list of firearms, and look at the wide variety of handguns and rifles used by the federal agencies.
A lot of H&K carbines and rifles are used which would explain the creation of the new H&K plant near Columbus, GA. FN already has a plant in Columbia, SC and Beretta in MD. Of course Glock is in GA and SigSauer in NH.
I noted a lack of Smith/Walther P99s and very few 1911s in authorized use, which surprised me. The only 1911s were the FBI Springfield custom Bureau models.
In general the revolvers gave way to Smith autos which gave way to Glocks and Sigs. A lot of 9MM and 40 cal but almost no .45ACPs.
H&K and Colt carbines and rifles dominate, semi-auto and full auto.
The shotguns are the workhorse Remington 870s and the Winchester Defenders.