Precision shooters would define that as 1/2-3/4 of an inch (or less) at 100 yards. I would guess- never tried it- that ain't gonna happen with cast or plated bullets, especially at low velocity.
You might check out the following on cast bullets:
Especially the part that reads
A properly made barrel (with bullets seated from the muzzle) will shoot 10-shot groups at 200 yards that will average about 1 1/4 to 1 1/2 inches (or) less in diameter. . . .
In the early 1950's when in high school, I used to occasionally see an old man come to the local outdoor 100 yard range with his .32-40 chambered Schutzen rifle. Using a false muzzle and bullet starter then pushing his cast bullets swaged just perfect down atop a small charge of black powder, he would shoot 3/4 inch, sometimes better, 5-shot groups all the time at 100 yards. He used a wierd looking rest under the barrel and rested the stock toe on another bag.
I doubt folks these days want to load cast bullets from their modern rifle's muzzles.