Aside from the single rifle that is overpowered (and I apologize for missing that when I was proofreading), but what were the other issues you had? What, exactly, did you find "out of place"?
It's the anachronistic stuff. Lever guns, black powder, WW2... We care a lot about WW2 in real life because it was our last great all out war that reshaped the world. The sixth world's culture has been through so much since then, I don't think their culture would have the same attraction to WW2 and Wild West culture that we have. Sure, there will always be historians and collectors and that's fine, but those people are not Shadowrunners. They're the same people who do antique firearms collecting and WW2 reinactments now: Fat old men with too much money. People who live and die in the streets in secret operations (which is the core of Shadowrun's setting) don't take novelty hobby guns on missions, no matter how muh we from 2013 think they're cool.
Shadowrun is unique because of it's unique setting. There are other cyberpunk games, but none quite like Shadowrun: Man Meets Magic and Machine. If we print a bunch of lolrandom books and it becomes "Man Meets Magic and Machine and Civil War and WW2 if you get all the supplements" the result is watered down, diluted by trying to shoehorn in a bunch of stuff Sixth Worlders are highly unlikely to care about.
M1 garand is an iconic weapon for us because we care about WW2. Where are the iconic weapons from the great upheaval in the Shadowrun setting? What iconic weapons do Sixth Worlders hold in the same regard as we do Nazi weapons because they were used to oppress people before the Great Ghost Dance and are a huge iconic part of their history? Where are the weapons that are important to people of the culture of Shadowrun instead of ones important to people from 2013 in an alternate timeline where Shadowrun never happened?
I love Shadowrun. I just think that focusing on enriching the culture and setting of Shadowrun is far more important in Shadowrun books than diversifying it. If we wanted diversity, we could play GURPS. We want more content, sure, but we want more strongly Shadowrun content. We don't need to pay for stats for weapons from 1940 in our timeline. We want more weapons from Shadowrun.
I hope this feedback helps.