Mitchell has shot the 55gr CT ballistic tips under .3" at 100yds to answer that question, I haven't shot anything under 80gr myself, but my 243 Ultra Varmint shoots factory 100gr Power-Shoks into ½" at 100yds. 
Tim
Interesting. I don't have a Handi 243, but I just purchased a Thompson Center Icon, a (dare I say it? will I be kicked off?)
bolt action and it comes with an MOA or better guarantee, and they use 100 grain Power-Shoks to test it. Nice to have a fall back factory round.
It seems that 243s do better with a wider range of bullet size than most calibers. Nice for versatility.