There are more myths, errors and mis-information circulating concerning cast bullets than almost any other subject in handloading.
You will definitely have a different point of impact, but the same applies to different jacketed loads. Re-zeroing is not difficult. You will have severe difficulty in trying to duplicate factory jacketed ballistics with any kind of accuracy with most modern cartridges like the 7 Mag. I say "most modern rounds" because with the rarer large-caliber rounds like the .404, .416s of any flavor, and .458s etc., cast loads easily duplicate or exceed factory speeds. Mild rounds like the .30-30 can also at least approach factory speeds without undue complications.
Wheelweights are NOT too soft. Cast bullets do NOT "start coming apart" above a certain speed. Leading is NOT a certainty at any particular speed.
I have fired a long string of PURE LEAD bullets from my .416 Rigby at 2000 fps without leading and with a 2" group at 100 yards. I have fired the same 360-grain RCBS .416 bullet, cast from wheelweights, at over 2600 fps without leading. This speed is far too painful for me in the recoil department, and I have no intention of trying it again.
My hunting load for the .416 is a two-alloy softpoint with a pure-lead nose and wheelweight-metal shank. At 2100 fps, the load will consistently group TEN rounds in 1.5-2" at 100 yards, and is a practical 200-yard hunting proposition. Strings of over 500 cast rounds without cleaning have been fired in my M1A, and it was still functioning just fine.
Apart from the larger calibers, I believe that creating cast hunting loads that work as well as our great jacketed game bullets is impractical, if not actually impossible. However, for fun and practice, cast bullets are great! I'm casting for about 12 different rifle calibers, plus five or six handgun cartridges, and I'd be lost without this extension to the hobby. Forty years' casting under my belt now, and I still have a whole lot to learn and study in bullet-casting.
Come over to
www.cb.gunloads.com (this is the "Cast Boolits" site) and meet over 6,000 fine folks who cast their own.