I'm not saying this is a reason why you're seeing poor accuracy with heavy bullets but you should check the barrel twist with a cleaning rod.
If it comes up slower than 1 twist in 8", that would explain poor accuracy with heavy bullets. It might keyhole if it's bad enough.
Some times the wrong blank gets used or the barrel gets marked wrong.
As said by many, chrome lined barrels are not the best for accuracy, a 1.5 MOA chrome lined barrel is a good one.
If it comes up slower than 1 twist in 8", that would explain poor accuracy with heavy bullets. It might keyhole if it's bad enough.
Some times the wrong blank gets used or the barrel gets marked wrong.
As said by many, chrome lined barrels are not the best for accuracy, a 1.5 MOA chrome lined barrel is a good one.