Asking price for an HK in any caliber starts around $1800 and metal magazines aren't cheap either. Sig 550s cost even more and their magazines are even scarcer.
Given the funds, you could go for either a FN-FAL type firearm (7.62 mm Nato). High capacity magazines are still affordable (about $10 each). Just be mindful whether they're metric or inch. The FN-FAL remains one of the most ergonomic rifles and during its heydey, was adopted by over 50 nations. Go to the FN-FAL website to learn more.
If you want AR, Colt's are excellant quality, have a strong following, name recognition, but dubious politics (see our Legal Forum) with regards to supporting the Second Amendment. Bushmaster is also held in high regards, but ever since they've been on overload (5k units a month to meet skyrocketing demands), complaints are cropping up on the bulletin board (
http://www.ar15.com ). One thing about BM, it has received good reviews from J. Feamster and Zediker, both of whom reports that BM is liked by custom makers because their jigs (drilling and milling fixtures) produce are right. BM Customer Services generally rights wrongs so I wouldn't worry too much about a problem. I bought a lower and have converted it for a southpaw gun (Norgon ambidextrious magazine release and DPMS ambi-safety).
I myself have had good luck with DPMS (they made my southpaw upper).
There is one basic weakness of the AR design: aluminum magazine with weak feed lips. They're easily dented so be mindful when handling them. Other than that, they're reliable, fun and a blast to shoot.
Magazines on ARs aren't cheap and we're talking about $18-20 for a aluminum 20 rounder (they use to be $2 each before the hi-cap ban).
Last but not least are the AKs. Robust, reliable, absorbs lotsa punhishment. Can't recommend any particular brand but when shopping for 30 round mags, try to get the ones with a rib running down the backside. They're stronger. One thing about AKs though, I don't think they're very accurate when compared to an AR or FN.
One final consideration: ammo. All three guns are different calibers. Pick one which you can buy lotsa surplus ammo at an affordable price. Gives you more to practice with that way.
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