I use an endocervical brush!!!!
It's used in medicine (cervical cytology)and I have some freebies. It is like a tiny bottle brush, tapered nylon bristles and it is easily bendable so great for getting into inaccesible breech areas. Also v good for cleaning out the vent hole on Remmy 700 actions.
A similar type brush is available from dentist/chemist and used for cleaning between your teeth.
PM me and I will mail you a couple
D