Something short. Flat base, short tangent ogive. A lot of custom bench rest bullets for shorter range matches are shaped like that. Go to the JBM Ballistics site and use their stability calculator. You can also look up bullet lengths there. Ideally, you want a stability factor of about 1.5, but 1.4 to 1.7 is generally still excellent, and really well made bullets can still shoot well at higher numbers.
