I am a bit reassured to hear a few other people saying they feel the selection is overkill. Hearing that by and large, the exact guns you use does not make a huge impact on your success or failure in the game, makes me want to go and have another stab at it.
I like depth too, but I've always maintained that there comes a point where a game stops being fun to play when it goes too far into the realm of tedious (and largely meaningless) detail.
The main issue was that it was my first time playing, the resolution was eye-wateringly tiny and I felt like I was spending most of my time studying gun stats. I didn't know how important the correct equipment selection would turn out to be during the mission, I had a limited in-game budget and didn't want to make bad choices that would screw me over or make the game harder in the long run. In short, it was
intimidating, and after a few sessions I was still spending 20-30 minutes stuck in that bloody catalog screen, scanning reams of guns whose differences were seemingly invisible to me. It wasn't my idea of 'fun' at all.
I think I still have the game installed, so I might pick it up again and have another try. And I'll take the advice that's been given, focus less on stats and more on just calibre and price, and see how that goes. Thanks for the protips, guys.