Have you removed the extractor ,cleaned, and replaced the extractor spring yet ? How does the ejector look, and does it play well with its slot in the bolt?
Pull & closely inspect your locking piece.
What is your bolt gap?
These are 1/9 twist barrels so you can use both 55 & 62 grain no problem.Mine is accurate at range with 62 grain federal greentips.Steel or brass should not matter,just keep your fluting clean.My first time out with my ptr/c93 I had 140 flawless rounds no issues but I can partially attribute that to spending some time going over the rifle this past winter.