I finally got around to slugging my 20" blue Rossi 92 in 44 mag. This gun has never produced a respectable group with any ammo I've ever tried in it (cast, jacketed, mag, special). The best it's ever done is with the Lee 240 RN over 7.5 Unique in special brass and it barely managed to keep up with my 4-5/8 flattop at 25 yards off a rest. I've never slugged it before but measured 0.430" at the muzzle with calipers.
Anyways, I found a good soft 45 cal bullet and lubed it and the barrel up. I started pounding it into the muzzle and all went normally for the initial 2" inches. Then the bullet literally dropped for the next 15" inches. Then I had to start pounding on it again. Then I had to start REALLY pounding on it. I was using an 3/8" oak dowel rod and each hammer blow was only moving it less than a 1/4" each time. I finally hammered it all the way out and measured it at 0.428".
So basically I have a barrel with 0.428" at the chamber, probably 0.433"+ for the majority of the barrel, and then back down to 0.430 or so at the muzzle. No wonder this thing doesn't shoot! That also explains why soft 44 special bullets work the best. I think I'm done with Rossi's. Should I try fire lapping or just give up and try to enjoy the 4" groups at 25 yards? It's good enough for fast pace steel banging anyways.