Scubapro chrome plated brass regulators...

[Angelo Farina]

Seems like there’s a lot of variations in springs, without a micro adjuster we’re at the mercy of the spring.

I just installed two shims and was able to get close to 1.0

Perhaps not a lot of variation. I would say that sometimes one spring was found slightly out of spec.
In those old regs there was just ONE tuning point, the orifice. So when some component was slightly outside the geometrical tolerances, tuning perfectly was impossible.
You had either to change the affected part or accept a slightly mistuned reg.
Converting to BA alleviated the relevance of proper calibration of the spring, as now the large part of the force which pushes the poppet against the orifice comes from air pressure, not from the spring.

 

[axxel57]

If we're talking about decades old spring, of course there is a certain variety in length and strength, depending on the usage, storage and normal production variety.
I have lots of those 109 springs and hardly any two have the exact same length or felt strength.
For sure might be converting a 109 to BA generally not a bad idea......
But I would consider the Adjustment Screw of the 109s also as a tuning (adjustment) point.