Agree wt Njordi. As the skill list expands, what a particular skill can do narrows. This can actually hurt players. I think Ars 5 has a great balance. For the individual character who wants a skill not listed, I would either make it a specialty inside an existing skill or just make it up.
Uhm...well the point is that would require a SG to allow that. MuHe(Te) would change the wood into steel...but it would be steel. Not some kind of magical alloy that was a strong as steel and as dense/massive as wood. Also the question would be what sort of steel. European steel during most of the middle ages was fairly low carbon content...which worked well for them. And again...you would need to change virutally everything in the structure to allow it to survive the first shot. Not to mention I have no idea what would happen to your steel beam when it hits the stop...it is not flexible like wood so that would be a heck of a stress on the beam itself...and the stop, and the structure. Plus the extra mass of the beam would slow the whole thing down...but if the extra mass of the counter weight would counterbalance that...really though you need to do some calculations to see if you gain from this. I am well dubious that you do.
Steel is a fascinating subject...I studied some of this in my course on ancient science and technology but to remain in period you would likely find that it isn't the modern wonder that we expect. Modern steels significantly outperform the stuff from the middle ages. Frankly, a good bronze weapon was better than most early steel ones but bronze was hideously expensive since tin was so rare.
Also you have to consider that even though the mage can alter things unless you have a generous SG you should consider that what you alter it to is within limits as well. The steel will be the steel a mage knows. I would think that essential nature will show up here...Steel is essentially steel...so wood transformed into steel has to obey the essential nature of steel.
This is my view...frankly this is really something that is more up to your SG and what he will allow then anything else. Its not quite a grey rule spot but its fairly close.
I suggest these stats:
Composite bow, skill: bows, Init -1, Att +4, Def 0, Dam +7, Str 0, Range 30m, Cost Expensive.
Tests showed roughly equal range (180-200 meters in the case of warbows) and similar power than the English long bows. The damage is the only question for me, I do not know yet the weight of the arrows of composite bows. If they are the same like the English longbows the damage code have to be also the same.
I used the stats of swords (long) to sabres.
To change a wooden bow to be like steel...
Muto Herbam just covers changing wood into other things. Muto Terram, however, covers changing solid objects in general, and allows manipulation of properties rather than just changing things into other natural materials.
Thus, a Muto Terram(Herbam) spell could make wood that is, unnaturally, as strong as steel. I would consider wood to be somewhere between clay and stone, as far as difficulty, so I'll go with the higher cost and assume that's a +1 as per Muto Terram... Edit: Of course, we're adding a property of steel, which is a +2, so that supersedes it I guess.
Muto Terram base 4 lets you change something so that is highly unnatural ('requisites will often be required' suggests that it allows changing something to have properties of another element -- precisely what we want.)... add +1 because it's wood and add a Herbam requisite, and you get Muto Terram(Herbam) base 5. Edit: Base 10, because properties of a metal make it +2, not +1 magnitude.
I think it would still be unusable because of thickness, as other people say, though it would at least bend rather than break and would be nice for anyone so insanely strong that they could use it.
With another magnitude to change the bow's proportions, plus a Creo requisite for the perfection of detail it would need, and maybe a finesse roll to do it properly, I would allow it to be a magically superior bow, and as a rough guideline I'd probably treat it like a Verditius Item of Quality, applying the +5 shape and material bonus 'Destroy Things at a Distance' to damage rolls with it.
Oh. Depending on what bowstrings are made of, it might need an Animal requisite or something, too. I don't know.