What can be a good substitute for saltpeter/potassium nitrate?

Question

in rocketry/pyrotechnics, what could be a decent substitute for saltpeter/potassium nitrate besides tree stump remover?

if you need to know, I'm trying to make black powder and some smoke bombs for a party.

Answer 1

Potassium chlorate.

Answer 2

iron oxide

Answer 3

I'm going to assume you can't use other nitrates; sodium nitrate, strontium nitrate, and barium nitrate all find uses in pyrotechnics.  Sodium nitrate in particular should substitute well for the uses you are considering.

Iron oxide is too weak of an oxidizer unless reacting with aluminum, magnesium, or another very active metal (which will make thermite - not a good choice for a rocket or smoke bomb).

Potassium chlorate will work in some instances, but is extremely unstable in compositions that contain sulfur - do not use it in black powder.  It will work in smoke bombs, and unlike potassium nitrate can be used in colored smoke bombs.  It will not be direct substitute; look up a chlorate smoke bomb recipe instead of using one for potassium nitrate.

Potassium perchlorate can also replace potassium nitrate in many uses - it even makes a similar composition to black powder when mixed with charcoal and sulfur - and is much more stable than potassium chlorate.  This would be my recommendation (assuming no sodium nitrate); but the best chemical depends upon the specific application.  Ammonium perchlorate may also work for you.

EDIT: To address your concern, potassium nitrate is probably one of the easiest-to-obtain oxidizers, so this is the one most likely to be found in common places (some drug- and grocery stores do stock it; if you get funny looks, say it's for curing meat).  Ammonium nitrate might be found in a gardening supply store (very unlikely due to concerns about terrorism), and while it can be used in smoke bombs, it is too hygroscopic (absorbs water from the air) to be used widely in pyrotechnics.