Mcbride, how would using a bunsen burner change the size of the nozzle? and if it would change it would only be by a small marginal.
when i cleaned my hotends with a bunsen burner i just ignited the abs and waited for it to burn out and then clean out the remains with the burner.
also you wont melt the brass as this has a very high melting temperature compared to the burning temperature of the abs....

DISCLAIMER, Do not under any circumstances do this inside!