Easiest way to tell cast vs. forged anything is to look at any lettering. On a cast part, any lettering that will always be placed on the part such as the words safe and fire by the selector or the 'up' on a front sight base will usually be included in the mold, while with a forged part all of the lettering has to be stamped.
- if the lettering is raised, you can be sure that it's cast.
- if all of the lettering that is pressed into the metal looks coarse, then it is probably cast.
- if all of the lettering is stamped into the metal then you can be 99% sure that it is forged.
I have two cast DPMS lowers and one forged DPMS lower, and the difference is obvious when you compare the lettering of the two. That, and the forged lower has the cat head logo roll stamped into the mag well while the cast lowers have a different logo that is obviously part of the mold.
The performance, fit, finish, etc. of the different lowers is identical.