Yes they are quite accurate in 45-70 and would be in any caliber, when used with light loads as they are intended to be used. Parlor loads they used to be called.
I can make similar bullets for any caliber 22 to 50, but cannot get the groove as deep, due to my boring process. Yet, I believe a better way to concerve lead is to make up a bullet trap. I welded one up many years ago, using 3/8 plate for the bullet to impact on, with about a 45 deg angle for the bullets to hit. They then slid along that surface around a curve and impacted on a 3/8 bottom. Rest of the trap was 1/4 inch steel. I made it for practice with a 22 auto pistol before I went home from work, so it sat in the machine shop waiting till everyone else went home. A co-worker brought a 45-70 in one day and tripped a round off into the trap and it wasn't dented, because by then it had probably 1 1/2 inches of spent 22 bullets laying in the bottom. - I had never thought of that trap since I quit the job in 1980 till now! I forgot and left it there!
There are several real important advantages of using full sized bullets, for your low velocity practice. Sight setting will be closer to your working loads, no special mold is needed, the report will be milder at a given speed, because the heavier bullet causes cleaner powder burn, and if you catch them in a trap you'll save all the lead, whereas a light bullet will save maybe only half. I've seen commercially made traps available, for probably about the price of one of my molds, and you can shoot all your guns into it, with light lead loads. If you use it with heavier bullets than the manufacture recommends, just leave a heavy layer of spent bullets in the bottom and watch the impact area for denting. If your loads dent it at all, back off on the charge till they don't.
