I'm planning to get some of those 277V F40 ballasts that veryhighonoutput was offering and since shipping is going to be somewhat expensive I just wanted to make sure one thing. Can 277V 60Hz magnetic rapid start ballast operate on 230v 50hz okay. I remember hearing so but just wanted to be sure. Does the powerfactor have something to do with it?

The magnetic part alone will be fine, the lower reactance at lower frequency is about compensated by the lower voltage, sbut that is not all.
There are two problems what may arise:
First the lower voltage will cause lower OCV available for the lamp ignition, so the lamps may have problems starting.
Second the ballasts use to contain capacitors as well and with many designs count on their impedance for ballasting. And because the voltage is about 20% lower, plus the capacitive reactance 20% higher, you get the arc current in the phase lead leg about 40% lower than intended.

So for an answer: It would be OK to run inductive only 277V/60Hz rated ballast on 230V/50Hz (e.g. a preheat series choke type), but once it contains capacitors as the main design elements (as most HPF RS ballasts do), it wont work correctly at all.

The specification term "magnetic" is really misleading amd this is the case, where it causes problems...

And it does not matter whether it's single or dual lamp ballast?

Some of our members from Oceania, I believe specifically member rapidstart, has some that came from the USA and I believe they work on 230V/50Hz mains over there. You might want to check with him before going ahead with this.

And it does not matter whether it's single or dual lamp ballast?

A single lamp HPF RS usually uses ballasting capacitor, so it will most likely underpower the lamp (lower voltage on top of higher ballasting impedance).

Double lamp ballasts use to be of two kinds:
One type uses just single arc current circuit ballasted by a capacitor, with both lamps powered in series. This will behave the same way as the single lamp ballast.
The other type uses capacitive ballasting for one lamp (so this will be underpowered like with the single lamp ballast), the second lamp circuit then uses inductive ballasting and that will most likely operate at full power (the lowre frequency will cause the inductive reactance to become lower, compensating out the lower voltage).

But at 230V I do not see much use to really insist on using US ballasts. You may make your own RS ballast from components designed to operate the lamps at 230V/50Hz:
You need the standard "preheat" series ballast choke, for a lead circuit a 3.4uF/450VAC motor run capacitor and then a 230V/2x4.5V transformer (with the secondaries insulated from each other).
From the mains you connect the ballasting coil in series with the capacitor (capacitor is optional) in series with the lamp (one pin from each end) and then use the 230V/2x4.5V transformer to get heating supply for the filaments.
In the US ballasts is nothing else (beside the step up transformer function for the 120V input types), only the series inductances are integrated within the step up (/down for the 277V case) transformer in the form of magnetic shunts and not as separate components.
On 230V you do not need any voltage step up/down, you need just the series inductances (hence the chokes)...

Well the fanciness was the only thing why I would wanted to do it. Like there was no other reason than cool-factor. It would also be nice to have it all neatly packet inside one casing vs. DIY with separated components.

But thank you very much for answering.

I think rapid-start ballast is the type of ballast with the highest losses from all types of ballasts, since it uses a separate transformer to continuously heat the electrodes before, during and after the ignition, rather than using the choke itself (By a starter) only to preheat the electrodes before the ignition, than rely on the heat from the discharge to keep the electrodes in thermionic emission temperature after the ignition.
In rapid-start, the "preheat" losses being consumed all the time the lamp working, in contrast to series choke and starter, where the preheat loses is consumed only before the ignition.

But at 230V I do not see much use to really insist on using US ballasts. You may make your own RS ballast from components designed to operate the lamps at 230V/50Hz:
You need the standard "preheat" series ballast choke, for a lead circuit a 3.4uF/450VAC motor run capacitor and then a 230V/2x4.5V transformer (with the secondaries insulated from each other).
From the mains you connect the ballasting coil in series with the capacitor (capacitor is optional) in series with the lamp (one pin from each end) and then use the 230V/2x4.5V transformer to get heating supply for the filaments.
In the US ballasts is nothing else (beside the step up transformer function for the 120V input types), only the series inductances are integrated within the step up (/down for the 277V case) transformer in the form of magnetic shunts and not as separate components.
On 230V you do not need any voltage step up/down, you need just the series inductances (hence the chokes)...

What if i take the heating supply after the choke too ? So that the heating is dropped once the lamp lights. (but it will lower a bit the available voltage for striking too so maybe make harder to strike)