Use any load that you find that equals 30-30 performance and it will feel like a 30-30, if thats the kind of 'reduction' he wants.
For less than even that use the Lyman Cast Bullet Handbook data to make wonderful cast bullet loads, but be advised that the same dia. as jacketed (ie, .308) is not what you want to use; you will have better luck with .311ish even cast of wheel weights with a dash of tin. At 1250-1400fsp, or so, gas checks may not even be needed on a GC design bullet if it fits the throat well, as that recommended .311 will likely do.