You can expect exceptional accuracy from your USAK as long as you find the load it likes.
Here's a link to a few targets shot with my now 5yr old USAK:
http://community.webshots.com/album/66414501RJKYArAs far as specific bullet choices, other than those PR bullets in the pics, I've had great results with Hornaday's 300gr XTPMags & SSTs over 80gr of 2fg 777 loose powder. The first 3 SSTs I shot with that load all hit the same hole at 50yds - that was all I needed to shoot. :grin: And the XTPs are my baseline bullet, anything that doesn't shoot at least as good as they do, go to the back of the range box for later plinking only.
I've found the keys to getting good results with mine to be:
1) Heavier bullets work best.....300gr to 400gr give better accuracy
2) Stay away from "magnum" powder loads. If you read the comments on those pics, you'll see my preferred charges are 80gr of 777 with 300gr bullets, 90gr with 350gr bullets, & 100gr with 400gr bullets. All of these loads run about 1500fps from the muzzle - which seems to be what the rifle likes best.
3) Accurize the barrel before getting "serious" on grouping. This can be done by shooting 20 to 30 lead conical bullets or patched round balls or by working 8 to 10 patches of a cleaning paste (like J-Bs, Iosso, Flitz, etc) through it and then cleaning it well afterwards. Either method will take care of any rough spots in the bore and have it ready to group well.
I too have a 1.5X 4.5 scope on mine which has been just fine up until now since my hunting area was shorter distances. Personally, I think a 2X7 would be about the perfect range for muzzleloading..................so your 3X9 is close to that mark as long as you don't have any WAY up close opportunities. Even then, if you use see thru mounts (like I do) you won't miss the shot.