JoJo
There are a couple of different Polymer lowers available in 80%. If you are going to go that route make sure that you get one that has proper reinforcement in some few area. The weak point on most polymer AR lowers is the buffer tube extension joint. If the 80% lower you are using doesn't have metal treads and some reinforcement in that area do not bother with it. At the price difference I usually suggest people go with an aluminum 80% lower. I unfortunately don't have any Jigs to send around. I plotted the AR lower into a 5axis HAAS. It takes about 10 min to complete a lower.....while I drink a beer.
Chris