since lead tipped bullets can easily be deformed in packaging and production it's not going ot be uncommon if measuring from the end to the base for them to be different lengths...

as said you can invest in the stoney point gauges... or if you have access to a drill press or lathe you can make your own... all i do for a given caliber to gauge off of the o-give rather than the tip is take a piece of aluminum or mild steel round stock, face both ends and drill a hole through the middle that is about 0.100 smaller than the diameter of the bullet. I then drill a hole about half the way through that is a thou or so larger than the bullet diameter... once you seat, slip it over and measure with the calipers, etc...

for my bolt guns i do the ole dent the mouth, blacken a bullet seat lightly in the case... chamber it and eject.. generally i have to pop the bullet out iwth a cleaning rod... reassemble in the case to the mark made on the bullet, then measure to achieve a datum measurement... and seat deeper accordingly...

Jamie