Paddler is right, Cran Dubh. The scale of a flute is a body thing; the head is made adjustable merely to allow for variability in embouchure approach, environmental factors, etc. If the body is made so that the flute plays nicely in tune at say 430Hz, it’s going to be too long to play nicely at 440Hz. Get it in tune at the top of the tube (eg the A note), and the D will be too flat. Tune the D and the A will be too sharp.
Sometimes, you can take one of these old flutes and shorten the body scale. But it’s a job for a professional, and one with nerves of steel. You need to find ideally a few sections of the flute where you can snitch a few mm off.
Might be just below the G# pad on the LH section, but then you’re going to have to fix up the tenon.
Might be from the top of the RH section, but then you have to deepen the socket. And will that then bring the Long F key touch too far up?
Might be below the 6th finger hole, or from the top of the foot, but will that bring the Eb, C# and C key touches too high?
And if the top of the foot, again we need to deepen the socket. Will that cause any problems?
Arrgghhhh!
Now, sometimes it isn’t quite that bad. Sometimes, the body is “more-or-less” OK at playing at 440, but the foot is far too long. This is what I have dubbed “Flat Foot Syndrome”. It was really a big thing back in Nicholson’s day, and my suspicion is that it came from opening up the finger holes, sharpening the body notes, but leaving the foot notes in their original places. Half an improvement.
You can recognise it by graphing the pitch of all the notes on the flute, with the flute tuned so A is 440. If most of the notes above the foot are OK, or are close enough to be tweaked, but the foot notes (Eb, D, C# and C) are dramatically flatter, then your flute is suffering “Flat Foot Syndrome”. Then you need to work out how to sharpen the foot. EG shortening the bottom of the RH section, top of the foot or both. But again, will that mean the foot key touches get in your way?
I sometimes wonder about having a cylinder of Helium with a delivery tube taped to the head of your flute. But it would make you sound a bit silly when discussing what set to play next at the session. That grand title, “The Bucks of Oranmore”, doesn’t sound so impressive if delivered an octave up.