is there a differnece between the stripped m16 lower vs the stripped ar15 lower or is it the internal parts that make the difference?

Some AR15 lowers wont accept auto sears due to a sear block or improper shelf height or material left in the wall.  M16 lowers have the hole for auto sears drilled.  Drilling the hole for the auto sear in an AR15 lower is construction of a machinegun.

All ar15 semi receivers (note that Colt made full-auto ar15's back in the day) that I have seen would require some machining to make room for the factory full auto sear in addition to having a hole drilled for the sear pin.  I'm not talking about sear blocks like those in late model Colts.

So, the answer to your question is "yes" - there are differences in the receivers.  There are some pics floating around that show the differences.

I wouldn't recommend putting m16 parts in an ar15 as the ATF frowns on this.  They have been able to make such a weapon fire automatically, and if they can do it with yours you may have won a $100K fine and 10 years in the pokey.   Full auto is kind of fun, but not that fun.

Joe

were can i find those pictures, i cant find with "search"

found it......