You get a couple of absolutely black patches out using Bore-Tek 'Eliminator', then the barrel is effectively clean. It does seem to reduce copper fouling as claimed. Cases-neck exterior surfaces are less fouled than those loaded and fired with Hodgdon extruded grades such as VarGet and H4350.
I'd expect to get the same MVs as H4350, but it does need a little more powder to achieve them.
I'm running 2721 from a 20" barrel with 140s. 43gr of the black stuff and a mag primer.I also switched from 4350 to the 4451 because I couldn't get 4350 in an 8lb container. My results match the data I found online. I can get the same velocities I was getting with 4350 though it takes an extra grain of powder. Even though I'm running an extra grain to get there I'm not seeing the occasional sign of pressure from the 4451 like I was with the 4350. Slight ejector marks. I read that the 4451 is better in regards to temperature change and lot numbers but that is only what I've read. Not my own findings.
I've been using 4451 in 6x47 Lapua, 6XC, 6.5x47L, & 260 Imp 30* for the past couple of years. Haven't had any H4350 to compare it to, but did run quite a bit of IMR 4350. Not a huge difference in accuracy or velocity, but in every case, in all four of these cartridges, 4451 was slightly superior to the IMR 4350, and way better when it came to temp sensitivity.
I run Lapua 123, Berger 140 LRBT & Hybrids w/4451 in my practical/tactical rifle, which has a 26" bbl. Running the 123s at 2880fps, 140s at 2780fps.