Bored so I shot a few targets with Eley Contact today at 50 yards and it was shooting pretty tight and about like I expected 1/2-3/4" or so, except one shot went about 1.5" to the right which was odd.
What is it that causes a single flier out of 25 shots like that?
Defective bullet?
Or something else.

I was single loading bullets.
The barrel has around 25 rounds on it since I last dry patched it and not enough for a carbon ring.