Wogpotter, I 've shot quite a few of your bullet #4 myself, and I bought the first SMLE I saw specifically because the bore was a multi-grooved, Lithgow-spawned thing of immaculate beauty (and the rest of the gun wasn't in bad shape either). It swallowed them uncomplainingly and gave me reasonable results (commensurate with my skill, at any rate). But I fully understand your problem.
Its actually not my problem at all. I have a tight '55 Faz that will eat BTs all day without compaining.
I was thinking of all those with Enfields that won't digest BT without a problem. (Thats not even my pic of the keyhole it came from someone else who was having the problem.)
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”