The top three American made scopes are leupold, us optics, primear reticles. The last one started out doing different reticles and boosting leupold scopes for a long time leupold would still uphold the warranty on a scope modified by premier. They stopped doing that and premier started making their own scopes. These are amazing scopes that trump leupold in every category. Of course they cost more as well with the cheapest one being in the $2000 to $2500 price range....
Talking to several vendors at SHOT most optical manufactures buy their glass from different sources in batches. Who ever best meets or exceeds the quality requirements for that batch is who they buy. I got that from leupold ziess and Swarovski as well.
There is also a group of 4 optical engineers in Japan who are hand jailing some amazing scopes that are taking the benchrest world by storm demon optics make march scopes. You can check them out at
www.kelbly.com