You are trying to substitute TM for lead in an already loaded shell, if I understand. As TM has not been available for hand loads, methods and load data may not be available.
I gather you are seeking a low pressure load, such as the Polywad Vintagers, and intend for the pressure to remain low after the substitution.
Ecotungsten's NiceShot is supposed to substitute for lead using lead load recipes per their site. It is a little harder than lead, but much softer than steel or the other tungsten alloy shot. You might want to ask both Polywad and Ecotungsten if the substitution is OK.
http://ecotungsten.com/shots.html .
Interesting that TM is a little softer than lead per Ecotungsten's link above. The substitution you originally proposed is probably OK.
