Re: OM string recommendations?
As others have said- the best string gauges will depend on the scale, your playing style, and your particular instrument. I believe there is a sweet spot where the strings are at an optimum thickness and tension to drive the instrument's best sound. Too thin and it feels "flabby"... like you have to push too hard to get the volume you want. Too thick, and it just feels like cables under your fingers and can overdrive the top... hard to describe, but you'll know it when you hear/feel that your instrument is maxxed out. Experiment with that, making very small changes each time you change strings, and see what feels and sounds best.
And to answer your other question - yes, as long as the strings' total length is long enough, bulk mando (or dola) strings will work on your OM. The strings aren't really different... it's just a matter of knowing the gauges, what type of ends you need, and how long you need. Make sure you measure from tailpiece to tuning post (and add some for a few turns around the post).
FWIW, pre-packaged mando sets are often cut shorter b/c they are being marketed for mandos. The bulk or single strings are generally longer, even at the same gauges, I assume b/c the manufacturers know that these might be used on a wide variety of instruments, including those with a longer scale.
Re: tuning in octaves- here's another vote for staying in unisons. If for no other reason than that it's harder to tune and stay in tune with octaves. Even if you play mostly chords, I think you'll find that there can be a lot of variation in intonation from the low to the high octave when they are side by side like that. In unison pairs, you can adjust the saddle compensation or bridge angle and dial in on the best spot. But when you have a low and high paired like that, they won't have the same best spot... at best, you have to compromise. Personally, I like the sound better too. Like with 12-string guitars, it's fun for a few days and then I find it's not worth the trade-offs.
Also- if you do go with octaves, you should expect to need a nut cut to those gauge specs. The notches for thicker strings may not serve the thinner strings properly.
Otter OM #1
Brian Dean OM #32
Old Wave Mandola #372
Phoenix Neoclassical #256
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