When I ran my tests about a couple years ago, the drops came as advertised, to within 0.2% (with a 2500 BOD sample, that's closer than I expected).
Do remember that there are bonuses for being 110 or 120 for turn ins.
(note that half are normal, half are exceptional. Apparently the 10% bonus that GM smiths were supposed to get to that either was never implemented, or accidentally lost. Also, 8% are supposed to be LBODs, but the existence of the non-combinables drops the effective number down to between 7.5% and 8%)
70-109.9 skill: 50% weapons, 25% Iron armor, 25% colored armor
110-119.9 skill: 50% weapons, 15% Iron armor, 35% colored armor
120 skill: 50% weapons, 5% Iron armor, 45% colored armor
The highest reward one can get from a small BOD is a 115 PS, with the highest desirable one being a Bronze Runic.
There are 24 "armor" small BODs, but that breaks down to 13 for LBODs, and 11 non-combinables.
Non-combinables and smalls for larges that have worthless rewards break down as follows-
1. Normal: most are junk, but...
a. Bronze 20-count & Gold 10 & 15, have a 20% chance for POF, if you have the ingots to burn (and if you use a lot of garg picks and prospector tools for mining, it's best to use the 20% POF BODs as the source, to reduce waste)
b. Gold 20-count & agapite 10 & 15, are the most desirable of the normals, being 90% POF, 10% +5 mining gloves (the latter, for your imbuer to play with, to get you decent pairs to wear or sell, which you'd enhance after imbuing to go for 140 luck for niter/saltpeter miners)
c. Keep 1 or 2 sets of 20-count Fencing weapon smalls for the off chance that you get an normal 20-count LBOD (iron's cheap, and this is one of the few iron LBODs that gives a POF chance). These are the only weapon BODs worth keeping.
d. Similarly, keep 1-2 sets of normal iron plate smalls for if their larges drop. The 10 & 15 counts have a 20% POF chance, the 20-count has a 90% chance. And, if you're not 120 yet, you can use filling these as part of your training regimen, turning in any extras for new BODs.
e. if you REALLY have dull or shadow ingots to waste, the normal ringmail LBODs of those metals have the same POF chance as the exceptional smalls of the same type (see below).
2. Exceptional BODs:
a. Dull Copper 10 & 15 count have a 20% chance of POF, but are so common as drops you could easily run yourself and ingot vendors out of DC if you fill them all.
b. DC 20 count, and Shadow 10 & 15 count, have 90% POF/10% glove chances.
c. Gold 15 count has 10% chance of the rare colored anvil, and a larger chance for a shadow hammer
d. Agapite 15 count has a 10% chance of an anvil as well, and a larger chance for a copper hammer
e. Agapite 20-count, and Verite 10 & 15, drop bronze hammers (used to craft recipe items to unravel for relic fragments).
f. the range between "b." & "c." drops DC & shadow hammers, for the people using them to make imbuing "blanks" (trying for desired or replacable mods, along with elemental damage)
g. the range between "c." & "d." gives copper hammers, which have a lesser chance of producing relic fragments by the same method listed in "e."
The chance for ANY COMBINABLE colored EX small armor BOD is
(percent from Smith skill) * 50%{the Ex chance) * 13/24
or
(12.5% * 13/24) for up to 109.9 (or, about 6.77%)
(17.5% * 13/24) for 110-119.9 (or, about 9.48%)
(22.5% * 13/24) for 120 (12.1875%)
for a specific metal, you'd then have to multiply by the chance of a drop. Number the metals, starting from the rarest down, 1 (valorite) through 8 (DC); multiply that number by 2.8% to get the approximate chance for that specific metal.
So, at 120 Smith, the chance for pulling a combinable Ex Valorite BOD is about 0.34% by the original rules (about 1 in 300 BOD pulls). However, the chance for pulling valorite was supposedly increased slightly (but not to the level of of verite) 5 or so years ago, so that could be as high as 0.5% (that's, on average, 1 in 200 BODs) - unsure of the exact amount.
Now, as to the commonality of Valorite hammers, while many of them for sale are dupes, there's also the fact that BODs from the Gold Hammer level and higher can get bumped 1 to 4 reward levels (at least, confirmed) randomly about 10-20% of the time, so that an Agapite hammer BOD could produce a Valorite hammer instead (or a Verite, or an ASH +60, etc). There's been one or two unconfirmed reports of a 5-step bump (gold hammer to Valorite), but again, that's without real confirmation. This has increased the supply for both legit and scripter/duper origin hammers.
Tailor BODs have similar factors, but have become dirt cheap from Barbed kits being about 100 times easier to get than Verite or Valorite hammers (half as many BODs, all combinable with larges, the top LBODs capable of 1-3 step bumps, and the guaranteed Barbed kit larges numbering EIGHTEEN, 2 of which are SPINED larges). On the other hand, there's NO reward worth getting from tailor smalls, and tailor BODs are only exceptional 1/3 of the time (instead of 1/2 like the smith BODs). The most desirable Tailor rewards are now not the Barbed runics, but clothing bless deeds (for use on tangle, crimson cincture, and a plethora of hats, sashes, cloaks, robes and footwear) - and those come from 5-part 20-count cloth & leather EX larges, and 6-part normal 20-count leather larges, as well as a number of higher larges (a total of 15 LBODs in all, only 2 of them Barbed leather). On some shards, it's gotten to the point to where barbed runics cost less than a CBD.