I'm trying my hand in making nozzleless "cohete" style rockets with tooling from woody's and instruction from Ned Gorski's video about such and I think I might be having an issue with the granulation process.
I am using 75/15/10 kno3/airfloat charcoal/sulfur all passing through a 100 mesh screen several times. To that I add 2% mineral oil suspended in 50ml of lacquer thinner. (not all at once) I work it into the powder thoroughly with my hands but when I try to compress it into a "putty ball" to push through my 20 mesh screen, it seems to break up very easily before it ever really takes "ball shape" no matter how wet or dry I have it. As soon as I press it against the screen it breaks up before I can fill the holes so what results seems to be inconsistent granule sizes and soft easy to crush granules. Do they get stronger the longer they dry? It's probably been drying for about 3-4 hours now. What am I doing wrong?
Most people do not granulate BP with a mineral oil/lacquer thinner mix. That would disperse your mineral oil, but probably would do less in consolidating the BP ingredients together to get not only a granule that's easier to work with, but also a BP that burns with increased speed. On a 1-10 scale of burning rate, I expect to get an increase of BP combustion speed of 1-1.5 additional units after granulation (I use 70% isopropyl for fast drying, but others use most or all water for cost savings). You can easily repowder and incorporate mineral oil afterwards. You might not be getting the burn rate increase that is a primary reason for granulating BP in the first place with your method, but it's easy to test. Burn a small pile of ungranulated BP next to the same mix after "granulation" and see if you get a speed increase. The mineral oil might complicate the comparison though, probably by slowing your burn rate... The only way to do an apples-to-apples comparison would be to do a dry incorporation of mineral oil alone vs w/solvent. You absolutely sure you even need to add mineral oil? And what's the quality of your charcoal (and thus, your BP) before even considering mineral oil addition or granulation? Is your BP satisfactory? If your charcoal is low-grade, then almost for certain your BP will be too, especially if you're relying on screen-mixing and not milling. And what is the fineness of your potassium nitrate?
A common theme with folks newer to the hobby is frustration with rockets and other devices because they haven't learned how to reliably make good hot BP. And not realizing when the BP batches they worked so hard on actually suck, and why, and how to fix this. This includes 100% of people who try to make functional BP from (overpriced) commercial BP "kits". And don't forget that Ned, although providing some decent tutorials and tips, has a vested financial interest in selling his info/website and promoting Skylighter's extortionately-priced chems/kits.
Good luck & have fun. Folks here are happy to help troubleshoot if you hit any snags.