If you are serious about writing, I suggest that you learn the difference between "due" and "do".
That will matter more than which gun is used.
I wish that I had a dollar for every time someone on a gun board uses "sight" for "site" or can't tell the difference between "to", "too" and "two." But most don't pretend to be writers.
As for the parents, I think a schoolteacher being married to a retired Army NCO is fairly unlikely. It probably happens, but I think I'd start over and make your character more believable. Gator had a good idea about the guy being a disabled vet, and that will get him reader sympathy. Gator has done some writing, and has a feel for such matters, BTW. And a vet might buy a Beretta like the one he carried in the military. If he was a CID agent, he'd have used a SIG P-228, known in the Army as the M-11. A medically retired CID agent might indeed become a PI. But check your state's requirements for a license!
In your previous thread, you were cautioned by one poster to write about what you know, and you clearly do not know guns well. And I doubt that you have the qualifications to write about crime.
HOWEVER...neither did Tony Hillerman or Robt. Parker work as cops or PI's and their books were VERY successful. They did know how to write plausible plots and good characters and settings. Same for John Sandford, who, like Hillerman, was a news reporter. Hillerman never knew zip about guns. He never even mentioned names or models of his protagonists' guns, although he could have easily gotten that from the Navaho Tribal Police. He probably didn't care, and may have even been mildly anti-gun!
Nevada Barr was a US Park Ranger, so she knows the guns she carried. Her books are about a fictional ranger. But Victoria Houston, who writes about a female police chief in Wisconsin just asked her local cops what they carry. (SIG P-226 in .40. But she sometimes has it in 9mm. She does discuss whether it might be replaced by a Glock, but thankfully, it wasn't.) I asked her if the recoil spring on the .40 might make it difficult for her heroine to use, but she told me that Lew is strong enough. I seriously doubt that Ms. Houston has ever retracted the slide on a SIG .40...the 9mm seems more likely. When we last spoke, the only gun the author owned was a Browning BSS shotgun. I think she hunts grouse with it. But she has taken flyfishing lessons from Joan Wulff and is a pretty good angler, so that part of her books is spot-on. Her series revolves around a chief who likes to fish with her boyfriend, a retired dentist. And Victoria knows the difference between fishing for trout and for muskies.
This may help: find a copy of, "Spiral", by David Lindsey. Read the scene where Sgt. Stuart Haydon shoots the Mexican who'd just murdered his partner. It is the best single scene of a real life type gunfight that I've read, other than one that I wrote for a book that I'm doing. (My scene is no better, just different.)
I respectfully suggest that you try to take a creative writing class or Journalism 101 at a junior college. You need better language skills, and you may get tips on commercial writing. And read some crime novels and try to get a feel for them and for spelling.
As for the guns, why not have the man use a snub S&W M-60 .38 (much more common than the three-inch version in .357) and maybe a Beretta 9mm for when he can carry the bigger gun? Or, have him use a M-66 .357, so as to have some ammo interchangibility?
You could do worse than study the late Robert B. Parker's Spenser and other series books. He eventually got the gun thing down pretty well, and his spare-but-elegant prose might inspire you.
But you MUST learn to write before you set out to produce a novel.
BTW, change the hero's name. Unless the guy is from the rural South, maybe Appalachia, Calvin is a name for a cartoon character.
T-Star