anyone have and issues with mag tactical lowers? im looking to pick one up for my ar47 build.  I know they are light but how durable are they or does anyone have complaints

I'm running one and I've had no problems, there have been a couple of reports of them breaking between the rear takedown pin and the receiver extension.

But being that they are castings, I think that there would be some failures do to porosity.

No problems with mine. Finish scratches easy

No issues at all on my light weight build.  

At one point, there was chatter about the gas key striking the extension hoop that was causing breakage.  As I recall, this was due to extensions, buffers and springs that were not mil spec quality.  The fix was limiting the buffer travel by dropping in a twang buster in the extension.  This keeps the gas key on the BCG from being able to touch the extension hoop.  Probably EvilBay parts builds...

I don't have a twang buster and mine is not even close at full travel, matches my forged and billet receivers exactly...

Most of that is internet regurgitation.