incomplete burning of thermite

the past several batches I've made would "explode" leaving allot of unburned thermite in the surrounding area. any ideas here?

Particles to fine? wrong ratio?

200 mesh al powder, and red Iron oxide dust, compressed into a canister.

How are you compressing it? If you are just pressing it down instead of shaking the canisters and tapping it on a hard surface you will trap air, this will force it apart. Plaster of Paris thermite works better because the products of the reaction are more sticky.

thank you!