If you're welding solid bar onto the end (which is preferable if you don't want it falling off), chamfer the edge of the bar you're welding on to the billet heavily, I like 3/4 round bar myself, nubs for the end so I can use tongs and still run through the rolling mill. I chamfer like half the diameter, so that when I make the first pass, it's the weld isn't protruding much past the original OD of the nub. Crank the voltage way up, and the wire speed has to go way up also, if it's sputtering or blobbing, or whatever, it's not set right. Consider that your billet is essentially like trying to single pass weld to whatever thickness that is, the minimum being whatever your handle or nub is. In the case of most "prosumer" 220 welders, i.e. 250 amp and lower, you could be running at max output and still not be too high voltage. If it's a 210 or 190 amp, definitely be near the top setting, then, build a puddle, and take your time going all the way around, then repeat on top of that weld you just ran, but running the puddle up and down so you're "painting" into the billet past where you previously welded, and the handle above the first weld. This should stack weld that ends up being wider now at the base, than the original OD of the handle.
I do this without pre-heating, and without removing mill scale, and haven't lost a handle in a very long time. The only point it gets tricky is once the nub has been run down through the rolling mill to 1/4" or so, and the billet restacked a time or two, but that's to be expected, and I'm just as likely to have the handle disintegrate somewhere beside the weld.
Just remember, the key, is establishing a puddle, and pushing or pulling that around, it's not like squirting hot glue. Higher voltage doesn't mean you have to be faster, in fact, take your time, and slow way down. If your weld is building up too fast, your voltage is too low.
Also, you want Argon/Co2 mixed gas, for MIG, but that's probably what you've got. Try to relax.
