I have an older 158 shotgun in 16 ga which was my first gun purchase I believe back around 1975 ( I purchased it at a Richway dept. store on sale for $38.00). I know in the iriginal paperwork that came with the gun I could have sent it back to the factory to be fitted with different barrels ( .22 hornet, 44 mag, 30-30, 45-70 I think) and would like to find some. Obviously, H&R 1871 won't do that with the older frames so I guess that Ii will need to find an original barrel on this board or maybe some other boards. My question - what is the real difference in these older frames vs the new ones ? metallury, dimensional ? Can I find some of the newer barrels and fit them to the older frames ( mild cartiges only) ? How much fitting is involved with any of these barrels ? Thanks for any feedback.