I was considering purchasing an AR 15 and wanted to know who makes the best one?

I dont know much about this particular firearm but shot a friends bushmaster and loved it. I want to scope one and maybe a match barrel. But I also want it to be easly adaptable to other configurations. Is it true that you can swap a few parts and change caliber? I was never especially fond of the 223 but since... show more I dont know much about this particular firearm but shot a friends bushmaster and loved it. I want to scope one and maybe a match barrel. But I also want it to be easly adaptable to other configurations. Is it true that you can swap a few parts and change caliber? I was never especially fond of the 223 but since its so abundant then I guess it wouldn't hurt. Any advice would be greatly apreciated.
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