5.45 AR keyholing

[Junkie]

I just put together a 5.45 AR.

I bought a barrel that had been drilled for the gas tube at the wrong angle, and drilled my own port (at the same distance).

It's marked: ST LW-19 CMV 5.45X38 1/8 QPQ MP

I took it to the range this morning to sight it in and every single round was keyholing at 25yd. Group size was maybe 3", not as bad as I'd expect for the rounds hitting sideways. This was using 7N6 surplus.

Is there something I'm doing wrong, or do I need a new barrel?

edit: it's not the same bore as a PSA 5.56 barrel I have - rounds, both 5.56 and 5.45, fit farther into the muzzle of the 5.56.