I'd think the MP-5 would be best suited for urban CQB for several reasons. It's got the versatility and response desired at close range battles. It's about 5lbs (depending one variation) but packs a mean 9mm rapid fire. F.B.I. uses the MP-5 chambered in 10mm, which is almost the equivalent as shooting the assailant with the Nascar 500
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I like the FN-P90. It's shorter than an MP-5 A1 and M4. It fires the 5.7X28mm round and holds about 50 bullets. Too bad only the Brits use it :\.
"I refuse to be outgunned by criminals!"