Kernman,
I don't really have an answer for that and I'll tell you why. I just got my USH a couple months ago and I was shooting cheap remingtons out of it. I started at 50 since the scope I had was already partially sighted in and I shot around 5 shots, 3 to sight in and 2 more for good measure. Then I went back to 100 yards and to where I made my mistake. I started shooting the cheap remingtons and was low of course, but when I tried to dial it in, they were going all over the place, so I shot around 20 rounds with no success. I was done for the day and only had the cheap remingtons. So for the next time I got back home to shoot I bought some Butch's Bore Shine, some hornady SST's, Remington Buckhammers, and some Remington Copper Solids. I cleaned about 90% of the leading from all of the cheapo's with the butch's then I re-zeroed it at 50' with the cheapos and moved back to 100 yards. I dialed it in with 2 buckhammers then put the rest of the box in a 2 inch circle. So I cannot tell you if the leading deteriorated accuracy or not since I never had it at 100 yards and never went back to 50 after all the shooting at 100, but I'm sure it was not helping accuracy. I never shot the other two brands because of how well the buckhammers shot. After that I left it ready for deer season and unfortunately did not get a chance to use it, maybe this weekend will bring better luck.
Matt