Before I did anything else I would do the same test with .303" Mk7 ball. I don't see how/where the red circle indicates a non round bore!!!!!! Where? If it's not round, then by definition it's not round around the whole circumference...... Or am I missing something?
Corwear WAS a known problem at the muzzles of rifles and always asked about at trade test times where you'd be asked to identify barrel faults. But I don't think I ever saw one in real life!
But with BSO's, we ALWAYS try a different batch of stock ammo before anything else