With a 1:14" twist it should shoot up to 55grn easily. Mine did anyway.
You sounded surprised saying it even shot 45grn extremely well!
My BSA was 1:16" and struggled with bullets heavier than 45grn. As did the CZ.
Of the three hornet's to pass through my hands, finding a load to go sub 1" was not hard at all.
Powders I used was;
H110,
A2400,
H4227,
BLC2,
Blue dot.
Bullets used were.
Speer 40 spire points,
Speer 50 TNT,
52 HP
52HPBT match.
Nosler BT in 40&50grn.
Sierra 40grn Hornet.
S&B 45 full patch.
The BSA was a nice well made rifle with a good bore,