rcmodel is on the spot with that. Its up to them what caliber you can carry in many occasions. Before my current desk job, the outfit I worked with was really wonky and, while allowing more freedom, were very strange in what could be used:
No .357 but you could carry .41 Mag or .44 Special.
No .45 Auto but .40 and .357 Sig was okay.
No "mouse gun calibers" but .380 and .32 Long was accepted (they were THAT specific on calibers).
They were at least kind enough to issue carry ammo, but practice stuff was purchased by the employee for the once a year qualifications (scariest time of my life considering the sweeping and pure foolishness of many of the other guards). The ammo usually given for carry was White Box JHP. Heck, one guy on the group carried .357 Sig, they didnt even give him JHP, 125gr. FMJ. Scary.
Check a list of approved calibers, but also GUNS too. The outfit we had said that you can carry a Glock (paid for by yourself) or they issue you a Smith model 13 (police trade in) or a Ruger P94 (beat to crap and very very worn, issued before the company even began). They stipulated even what kinds of guns you could have:
No Tanfolgios or EAAs, but a CZ was okay.
No Taurus, but in the handbook, the list of "encouraged" guns included a Taurus PT92.
1911s were not allowed as the administration running the company believed them "too unreliable with the amount of clones and parts available" (puke), however a FEW Para's were listed as okay (not that one could afford one on the amount paid for the job, but also no .45 models
).
Hi-Powers were allowed, but according to the rules, ANY single action gun was to be decocked and carried empty chamber, but no such rule for DAO or DA.
All weapons carried could NOT have night sights or ANY modifications (ZOINKS!), even a Hogue Handall on a early gen Glock was considered a modification.
Mags were to be loaded only to 10 rounds or 10 round mags used. Only 1 extra mag was alowed, but one could carry as many speedloaders as long as it didnt interfere with movement
D
).
Personally, I carried the 13 for a while, then bought a police trade in Smith 4006. They even took out of my check and I got to keep the 13 when I left (the 4006 was mine to begin with). When I left, the company pretty much was bought out by Loomis (good thing as I heard they were very restrictive on equipment, aka, you purchased it on their dollar so they told you what to buy).
ITs all up to them, but alot of the companies lately have been issueing/equipping/encouraging their members to get Glocks. I would assume that is due to control simplicity and easy to get/repair parts. Older Smith 3rd Gens and revolvers (Mostly Ruger GP100s and Smith 10s) are the norm for alot of other companies.