(Disclaimer: I don't have Fo4 yet, and probably won't for a while, since my current laptop just barely meets minimum spec, so I base this off screenshots and the limited info currently on wikis, which I know may be wrong/incomplete).
In one of the ads, we saw the Sole Survivor using what appeared to be the US Marines' EBR version of the M14 (https://en.wikipedia.org/wiki/Mk_14_Enhanced_Battle_Rifle). However, from the screenshots and wiki articles on falloutwiki.com and vault111.com, it doesn't seem the default Assault Rifle looks anything at all like this, it is completely fictional although perhaps bearing a slight resemblance to the XM8 (https://en.wikipedia.org/wiki/XM8_rifle) - the only thing that looks anything like a real weapon being a 10mm unique pistol that looks somewhat like a Walther PP and a .45 SMG which is obviously a Tommygun. Have they completely abandoned the weapon styles of FO3/NV in this game (the default 10mm pistol looks nothing like the one from F03..)?