Low B string gauge for a 24.75 scale seven string.

[ChristopherG]

So I decided to dick about with my Ibanez AX7's intonation since it is going to be at least a few months before I take her apart for her rebuild.

Once I got the action high enough on the low B to keep it from buzzing when attacked with something harder than dainty speed picking I started taking the saddle back. And back. And back. And back. All the way back. And it is still sharp at the 12th fret.

Currently that string is a .56

So do I go up or down in string gauge?

 

[TonyFlyingSquirrel]

That's what I use, has worked fine for 16 years.

 

[swarfrat]

Going up will only increase the tension and the stiffness both - requiring more compensation.  That's REALLY short scale for a 7 string. Even if you get it right, your enharmonicity is likely to be pretty crazy. In fact - if you're checking intonation with harmonics - that might be your problem.

http://www.sevenstring.org/forum/extended-range-guitars/10064-string-gauges-inharmonicity.html
"Not bad" on their scale for chordal tones might not be adequate for intonating the guitar.

 

[Ace Flibble]

It's pretty normal for the 7th string to run a little sharp. Most of the time you just tune it very slightly flat, so for fretted notes it is back in tune. Same issue short scale 6-string guitars run into when tuning low.
You can buy pre-cut 7-string Earvana compensated nuts which will get you closer to proper intonation; with a standard nut, I don't even bother trying. I set up all my 7s and low-tuned short scales with compensated nuts, and I set intonation on the lower strings by the fretted notes, not harmonics. Only people who will notice things are off are audio engineers with a strobe tuner on at all times. Nobody listening to a recording or watching live will hear anything amiss.