Can I say Barrett .50 cal without being chased down by an angry mob?
No, you'll be chased and beaten. Like I've said lots of times before, people get huffy when it comes to Fallout's lore and how the weapons fit in to it. Apparently every weapons designer got a knock on the head in the Fallout world and is incapable of making anything that looks futuristic, DESPITE the fact that Fallout's universe is supposed to be based on the futuristic ideas of people in the 50s.
Examples of 'futuristic' guns that were used in the 50's and 60's
http://upload.wikimedia.org/wikipedia/commons/e/e9/M60.jpg made in 1957
http://www.warboats.org/stonerordnotes/Stoner%2063%20R4%2011.jpg made in 1963
http://upload.wikimedia.org/wikipedia/commons/3/36/5064-04.jpg made in 1953
http://upload.wikimedia.org/wikipedia/commons/d/db/MAC10.jpg made in 1964
http://upload.wikimedia.org/wikipedia/commons/8/86/Uzi_1.jpg made in 1954
http://www.oldjoeinfirmary.com/images-vb/oji2761.jpg made in 1966
http://www.impactguns.com/store/media/colt_m16a1_mgt9223839.jpg made in 1963
http://upload.wikimedia.org/wikipedia/en/thumb/9/92/M203.jpg/300px-M203.jpg made in 1966
http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/MK19-02.jpg/300px-MK19-02.jpg made in 1966
http://upload.wikimedia.org/wikipedia/commons/b/be/HH-3-minigun-vietnam-19681710.gif made in 1963
http://upload.wikimedia.org/wikipedia/commons/9/9a/Machine_gun_M2_1.jpg
made in 1921So if people really want to have old weapons, there they are.