So yeah, I just spent $270+ on a part I've been dreaming about forever. The Magpul UBR stock. And I have absolutely no complaints about it at all. But my delton lower is a piece of non-mil spec crap. The ubr doesn't fit properly and leaves a gap between the lower and the main tube assembly on the ubr. So my dreams were a little crushed. But, I figured I've been needing to buy a new stripped lower for quite some time, seeing as my pmags don't drop out of the magwel and installing a miad kit required alot of force and a dremmell. My dad's friend showed me his Spike's zombie lower awhile ago and I want that. It's affordable at $115. I just wanted to tell everyone that delton needs to get there stuff together, and ARE SPIKES LOWERS MIL SPEC?
Btw the ubr will still function on the delton lower. The only problem is that because of the slight gap, it takes a little tension off of the rear takedown pin detent spring (which I broke during disassembly). So your rear pin will be a tiny bit looser.
Idk the proper term for the hole in the lower that causes the problem, and I'm too lazy to google it. But it's the small circular hole cut into the outside of the lower right under we're you screw in the buffer tube. The ubr main tube assembly has a circular piece that fits directly into the hole and keeps the ubr from spinning around. Delton made the hole too small and the ubr won't fit in. It sits of the edges of the hole but not in it.