I have a 2vets SOPMOD at. It's a side charging upper. The lower is milspec. I don't know if anyone here is familiar with 2vets if so, can a top charge upper be put on the lower if the lower is a milspec ? The buffer appears to be standard for an AR. I'm just curious. If I can I want to get a lower price upper or build one to use as a back up. I know that the bcg on the side charge is the same mill spec. Firing pin, bolt, gas tube. The only diff I can see is the way it's charged.