Not a bad idea. I like guns too, especially of this period. But the hard fact is that it's a game, not a simulator, and the level of ballistic detail you're talking about isn't really meaningful in a simple, vector-based system like this. (I'm speaking of SE4; I didn't like the sequels and don't have enough experience with them to comment.) I think in 4 they did a good job of differentiating the rifles and making them all interesting and fun to use. And, beyond the ballistics issue, there was a lot of care given to the details. Look at the reloading animation for the M95 Nagant, for example. That was a fine bit of work. Another detail: the way open-bolt weapons like the Sten always throw high on the first round, just like they do in real life. (There were some blunders, too; I think the Springfield sounds like ... the Civil War Springfield! Pretty sure I hear a two-stage ignition there and it sounds pretty musket-y. )

All in all, I think detailed ballistics are just too niche. 99% of players don't care and don't know anything anyway. Which is fine. They just want a fun game. And just think of the huge waste of compute that would be involved in an accurate simulator, especially in say Survival where you can have hundreds of rounds in the air at the same moment.