Re: AR-15 DISASSEMBLY?
If you have a collapsible buttstock. Be sure to back off the retaining nut and try and not turn the buffer tube. Its fairly easy to damage the rear takedown detent spring. Just back off nut and slide the plate back rotate the buffertube a little and pull out that spring on the back of the receiver. Also have the buffer and spring removed since the buffer retainer pin and spring will come flying out.
Unless you are trying to strip paint off a lower I would just clean one up by blasting it with gun scrubber or carb cleaner