As for the barrels fitting new receivers, it just depends. Some fit, some don't. I have an older Shikari barrel on a newer SB-2 receiver, it fits better than it did on the original. I have an older 410 barrel, doesn't fit anything I have. The old Topper 30-30 barrel I bought finally found a home on another SB-2 receiver, but it is the only one out of 6 that it fit. The underlugs on the older barrels are usually silver soldered on, so they are not for the high pressure stuff anyway. The 30-30, trapdoor level 45-70, and 357 are the limits.