If she is in proof; ascertainable by measuring the bore at 9" from the breech face, and the gun is tight and free from deep pitting she should be o.k. for 2 1/2" smokeless ammo. Standard load for these is around 13/16" ounce. It tends to defeat the object of having a lightweight English 20 bore to try to use heavier loads in it. Use light loads and enjoy the fast handling. Lagopus.....