Yes that’s the size of it most seedling callery rootstock don’t get fireblight. Rarely one does but genetically most are immune or resistant. Many say they live 20 years , get fireblight, have weak limbs, and other things none of which are true of the wild seedlings. A true Bradford does carry fireblight and have other issues. They are a beautiful tree which has made them so popular.
You can graft your Bradford over .
Yes Douglas is highly resistant to fireblight like its parents Kieffer and Duchess D’ Angoulme.