Couldnt have said it any better myself

.............should also mention that undersize lead bullets, especially evidenced by tumbling, will, well, lead your barrel; not conducive to accuracy. Hard, but undersize lead still leads, but soft bullets of the right dia. wont lead even if driven pretty fast. FME, you wont get much of a change in dia. by changing alloys in that 'small' a mould, but every little bit helps. Since you have it, why not cast up some softish (say, 50/50 wheelweights and soft lead) ,hand lube and use as cast dia., and (BTW, I dont generally like or use gas checks) and load them up to about a 1250+ fps level.
Please do try it and tell us what happens! Remember, all shootin' is practice, and the wisdom comes by the journey.