sub inch groups are done on a regular basis shooting lead bullets
some of the older rifles shoot better (smaller) groups shooting lead
1500-1800 fps can be done with lead base bullets
the limit is velocity 2000-2100 fps is done with out a lot of witch craft and potions (gas check)
2500 fps can be done by a apprentice to the casting craft from learning from a master (and having the right barrel twist)
to go faster you need a master caster (of the paper patch craft)
and it can be done with off the shelf rifles or 100 year old stuff
and even a semi auto can be used with lead bullets with full function
7.62x39 / 308 / 3006 to name a few with full semi function
If done right NO Leading or only a bit just look at the common 22 RF
1200 fps and how often do you really clean them and the powder in a 22 is dirty
but if you do the wrong thing you could be scrubbing out Lead or not hitting the barn (standing in side)
do your own research and don't listen to old wives tails