[Doyle]

With a little further research, I learned that some were m500s and some 590s. Apparently, 590s have barrels with heavier walls, better extractors, high cap mag s, etc., etc.

That's all part of it I guess, apparently the m500s just aren't as heavy duty.

Don't make the mistake of confusing some of the 590's "features" as any indication of extra "quality" or longevity. The M500 is plenty robust enough for many thousands of rounds.