very true. Aluminum wire is soft, no matter the grade. If you use it with your standard gun then you better make sure you have a new liner for it, and your cable is straight as you can get. Also, if you run it in your standard gun I'd suggest the 5356 stuff (I believe that's the grade, it's been a while so I may be off a little) because it is a harder/stiffer wire. What happens is your wire will "bird nest" in your liner if you're not careful. A spool gun makes it so instead of having the get pushed 5-10ft it's only pushed 6" and it's a straight shot. We had a push-pull setup at my old job, basically it allowed us to use a huge spool (40lb??) and would push it at the machine but we also had a gun that looked like a spool gun without the spool that would pull. Our cable was 25-30ft long. We also had another machine setup with just a spool gun, and even with both these setups we'd still get bird nesting so with them I imagine it would be very frustrating.
Never heard of an aluminum gun nor have I ever heard of preheating to weld aluminum. You should have a dedicated liner to the aluminum (if you use one that's been used with standard wire you'll get contaminated wire) and dedicated drive rollers are also a good idea (for the same reason). For cleaning, just get a good stainless steel hand brush and scrub the hell out of it. If you try to use a grinder you'll often just embed the impurities even deeper.
