well for bullpups, it's impossible to beat a FN Herstal FS2000, expensive and hard to find but overall it's probably the best one out there that's available to the public.
pistol caliber carbines like the beretta CX4 storm are great guns. accurate, well weighted, compact, and ammo capacity isn't horrible.
AK47 is another popular one though I think the days of sub-$1000 are well and truly gone, supply has dwindled, demand skyrocketed, now they are just expensive. IMHO, they are overrated anyway.
for me the AR15 is really the best way to go. it's hard to not find parts for them, you can slap a decent one together for less than $600, they are very accurate, triggers are mostly decent compared to other guns in this lineup, and controls are very easy to actuate/operate with your off hand while keeping firing hand firmly planted and without losing sight picture.
SKS is a decent second place in my opinion. simpler take down/reassembly than an AK47, more accurate(in my experience) than an AK47, well balanced, quite modular, and though not as easy to operate as the AR15, controls are easier to work around than a lot of other designs.
no experience with cetmes, fals and those other heavy, clunky semi auto battle rifles, I just can't convince myself to like them.
all guns lost in a tragic smelting accident.
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