Ammunition used by the Project should be as standardized as possible. This is also true of the weapons themselves but ammo is even more critical.

Modern tactics can use up a lot of ammunition very quickly, and the MP teams don't have the support organization(s) a modern military group does. Ammunition expenditure in a battle is often extremely high.

In the "Seven Day War" both Israel & the Arabs were critically low on ammunition by the third day! And if you think these folks didn't start off with a lot of ammo you're wrong. Israel was restocked with ammo from NATO stockpiles while the Arabs were from WP & other stocks, both in subtantial numbers. Ask most combat vets about what they carry on them, especially for long patrols, etc. and they'll usually say "lots of ammo, and water". You can skimp on nearly everything else.

Because of this critical need for ammunition, the teams are much better of with firearms that use the same ammo wherever possible. In my MP campaigns, handguns & SMGs all use the 10mm Auto round, loaded to moderate levels (180gr @ 1200fps from pistols) for an E-Factor of 10. While in E-Factor terms this is a very minor improvement over the 9x19mm, that's because the most serious flaw with E-Factors is they don't take bullet weight into account. In real life the difference is more substantial. The PD will have to exercise his own judgment here on what the standard round should be, but the choices should probably be limited to the 9x19, .40S&W, 10mm Auto, or the .45ACP.

I do make one minor complication to the pistol/SMG standard ammo issue, which is to give some subsonc, heavier bullet 10mm ammo if the team has any suppressed weapons like the MP5SD3.

The only other cartridges issued are the 5.56NATO, the 7.62mmNATO, and the .50BMG. I let team pick the specific weapons they want in these calibers for their basic loads, and most teams standardize on their own for the most part. Of course, they can bring weapons in other calibers for any weapons in their personal gear locker, but they're on their own as far as ammo supply goes. The PD can make exceptions as he sees fit of course. The personal gear space must also be used if for some reason a person can't use a 10mm handgun, but I have yet to see that exception come into play.