I started making my own checks from al. and get better accuracy with them than Hornady copper checks.
I did have to experiment to get the right thickness to make them from. I finally settled on .014 flashing from Ace Hardware for my 35 whelen. Further experimenting proved to me they needed heat treating to shoot their best in my rifle...that may differ from one rifle to the next. Actually i just heat them for one hour @ 400* so their not truly annealed, but it works for me. They size on tighter after annealing.
It took about a month of testing different thickness in material but was well worth it for me.
I have never seen any residue from al. in my bbl. They don't come off in flight that i can tell and definitly group tighter than commercial checks for me.
Al. checks work but may take a bit of trial and error to find the best thickness for a given rifle or hand gun.
Btw..i couldn't get mine to shoot well at over about 1900 fps. before annealing. After that they shoot well at any speed up to 2400 fps + so far with the right load and boolit. Probably depends on the hardness of the al. as to whether they need annealing or not.