Normally you'd expect the DPMS to also have a commercial diameter tube. Sounds like this one has the smaller diameter milspec tube which would cause a sloppy fit using a stock for the larger size.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek