All centerfire H&R rifle barrels are 4140 alloy except the stainless barrels, they all have 1.1XX" diameter chambers, the 270 Win is a factory available chambering with a SAAMI MAP of 65kpsi, so the 357mag can be safely rechambered to any suitable non-magnum rifle chambering as long as it's on an SB2 rifle frame, 358 Win and 35 Whelen would be a couple high pressure options. H&R started just this year offering 357mag and 44mag rifles on SB1 shotgun frames, neither of those would be safe rechambers to higher pressure rounds. The 357mag has a SAAMI MAP of 35kpsi, the 357Maximum's SAAMI MAP is 40kpsi. The Max may work fine, but many here that have tried the Max on SB1 frames had perforated primer issues due to the larger firing pin and surrounding hole in the SB1 frame.
Tim