JohnP,
Did you ever find out the spring wire diameter for your 350?
I've addressed your pellet questions before, perhaps you didn't see my feedback.
Much will lie on the size, so you don't cause undue stress.
14.2 gr will be OK. I shoot several near that weight.
I wouldn't go much less though, or over 16gr until we know the diameter.
I've asked this question elsewhere but no answer yet.