One of my oldest friends is an AM.
Their duty round comes in a Speer box, 125 grain Gold Dot. Nickel cases, primer is a darker color than the case.
They are authorized to carry two different guns. SIG 229 was the standard and only one for a long time. But there was a lot of lobbying for a smaller gun, one that could also be more easily carried off duty. So they are also authorized to buy and carry 239's. There was a plan to switch everybody to the 250 but, sadly for SIG, that design failed during their testing. The AM's who were involved in the testing recommended that it not be adopted. I haven't talked to my buddy in a while since he lives hundreds of miles away so I don't know if anything has changed in that area.
He carries a 229. When we were younger and had both recently gotten out of the active military, I used to be able to outshoot him with a pistol. That's very untrue today. The AM's do a lot of training. Lots of shooting, lots of hand to hand. He is one of the best pistol shooters now that I've ever seen. The people I've seen shoot better get paid to be professionals by sponsors at shooting events.
It's true the .357 SIG was picked because that's what the parent agency was using. Lots of people thought they should have gone with something wider and slower but it seems like most of them today are happy with the choice. They are deadly with it.
I own quite a few of them myself. Including an AR that uses Glock mags. A Glock 35 with custom barrel. Two HK P2000's. (Daily carry gun is one of the HK's.) I reload for it. And whoever said it before is right... fired brass is cheap. Even the good stuff. Even cheaper if you have an AM friend. Between buying bulk 9mm bullets and free brass, I can shoot it cheaply.
I'm a huge .357 SIG fan!