Is the gun atypical?
First of all, let's start our quest in the Corebook. Looking for .357 gets us 6 mentions in the book at all, the first mentions in the item catalogue on page 66 (the other 3 in descriptions):
S&W Combat Magnum - P 1 J C 2D6+3(.357) 6 2 VR
C.O.P. .357 Derringer - P 0 P C 2D6+3(.357) 4 2 VR
Hot Loads are not mentioned at all. So here we jsut can pick up the baseline of .357 damage, not anything about Hot Loads. Now, where does the Hot Load come from? Let's search books...
Chromebook 2 comes up with new ammo on page 46 and following, yet while it has DP, API, rubber, flechette and ET ammo, Hot Load is not here. Next!
Next up, the Blackhand's Street Weapons, page 12 has the following:
Nomad .357 Magnum Autoloader - P 0 J C 2D6+3(.357) 8 2 VR
This is almost the same as the other two examples from the core book, yet it is not the Hot Loaded variant on which the book claims to "see below". So below we look (finding the revolver variant on the next page) and come to page 43, titled "Ammunition", yet Hot Load is not listed there, and most of that stuff here is a carbon copy of the Chromebook 2. So where does the new line (it isn't in NeoTribes on page 64, that I can confirm) come from?
Let's look at the publication timeline...
NeoTribes claims in the foreward to come out in January 1995, the RPGnet Entry dates 1994.
Blackhands Street Weapons again read 1995 in the front, its RPGnet Entry dates 1994. And then there is this tiny bit in the review:
Some weapons have had their stats corrected, some quite dramatically [...] Also some of the books it sites as sources don't seem to be correct(where are hollowpoints in CB1 or CB2?)
Ok, so there might be a Hot Load thing somewhere... but where?
Search for hot load
Next book... Corpbook 2&3 had nothing, neither Eurosource or Hardwired nor Home of the Brave nor Interface Magazine nor Maximum Metal nor Solo of Fortune 2 nor any other book I found in my collection...
I even dug out Andrew James Cyberpunk 2020 Reference Guide v5, a fan project dated "5th January 2002" - and it has not even an entry for "hot load".
So, to come back to the question: after reading through any non-adventure book I had, I could not find another mentioning of Hot loaded ammo at all. NOT checked by me are: Solo of Fortune (1), Rockerboy, Near Orbit/Deep Space, Interface V2#2.
It might be a case that this hot load sencence was one of these "updates" on weapons, it might be a forgotten thing that never was put into the final book, but I can't seem to find any different source for hot loaded .357 doing more damage than 2d6+3 - in fact, that is the supposed regular damage for a .357 according to th examples in the core book.