Choice of root canal filling technique

Doctor, sometimes I cannot perform lateral condensation even though I want to. If I finish with 25/06, a 30/06 master cone generally binds at length. When I then want to place an accessory cone, I cannot even insert a 20 spreader into the canal. Sometimes, when I apply a lot of force, the spreader penetrates the master cone and pulls the gutta-percha back out. Is there any objection to using a single cone in these situations? Because our gutta-percha cones do not match, 25/06 usually extends beyond the apex.

Translated version of the Turkish original