I fly a lot of Estes type low/mid-power models, kits and scratch-build. Generally up to about G impulse. I also hand-ram BP motors for these, with good success. Without a press, you'll never get the grain densities that a press will give you, and your motors will generally be larger than an equivalent Estes, but cost about 5-10% as much once you dial things in. And you can make them as big as you want!!!
For finned rockets, BP motors such as Estes are endburners or else have a short core. For example, the same-dimension 24mm-diameter Fat C11 motors and D12 motors are packed in the exact same tube but the D12 has a little deeper coring and more initial "oomph" (would have to get out calipers to see if there's nozzle differences, too). With APCP composite motors, they are fully cored and need ignition at the very top end of the core to function properly.
Regular fireworking coreburners will rip the fins of of most low/mid power kit model rockets unless they''re majorly reinforced (aircraft plywood fins instead of balsa; TTW construction; thick fillets; reinforced motor mount; body tube reinforcement on longer ones). It's definitely doable. Endburners typically use a hot 75% BP whereas fireworking coreburners often use a cooler 60-65% BP (% is KNO3, btw). I regularly make 1lb (3/4" inner diameter) motors for finned models and they work great. You can also make smaller ones with 1/2" tubes--18 mm outer diameter like Estes A-C motors.
Two good resources for this kind of project are Gorski's article over at Skylighter, where he tried to recreate I think D motors: https://www.skylight...-rocket-engines . Good advice is not to repeat his wasted time using crappy commercial hardwood airfloat charcoal at all and go straight to a hot BP made with a hot charcoal (ERC is simple to make or to purchase). I think he only used screenmixed BP, but I get better results with damp granulating (no binder!) before ramming. Less of a mess and the ingredients get better incorporated. If your powder/granules are dry, then moisten with 2% water before ramming or pressing for better compaction. Another good reference is to look up the threads on this site started by member "hcb". He also has some Youtube videos of an Estes Patriot missile flying (and popping it's parachute for safe recovery) on a homemade C+ equivalent motor. I can fill in any details.