With the extra clearance what kind of accuracy are you expecting. Most rifles don't have lands much more than .004" high (on each side) so you could end up with some funny looking holes in the target. Also, depending on the type of powder you use, leading may be an issue with all the hot gas leaking by the bullet while still in the bore.
I know guys who've used 9mm bullets in .38/.357's as well as .357 bullets in 9mm's but that's only .002" at most. A whole .020"???? You may lose interest in this new round very quick.