Yours in the on the lathe at the moment but it is past the point where it can be shortened. You can wait for the next brass one and I'll size it for 18500 or you can have the copper in that size, or both. Whichever you would like I can do.
A note on the 18500s, I like runtime while preserving the ability for occasional use of the 3 amp high. As such I designed the 18500 to accept the 53mm 1700mAh Keeppowers which are protected cells based on a Sanyo cell. Shorter IMRs might require a magnet spacer for a reliable connection.
Yeah, I'm running two magnets (totaling a quarter inch) with an AW IMR 18500...