I get precise when I'm making tri lams. Fractions don't cut it for me, sorry Roy.
I use .190" with a .002"/inch taper for all of my cores to keep it constant, and I adjust my belly lam when trying to hit different weights.
Not sure how much I can help if you don't have an accurate way to taper your cores. It's just not the way I do it.
If I had the wood you do, I would do the following: bamboo - .125" tapered approximately 0.002/inch
Lemon core- .190" tapered 0.002"
Ipe core- .25" tapered 0.002"
That would get you close to 50-55 lbs depending on bow length, width, riser length, etc. etc.
Other's may have better options for you.