Guns for anachronistic ships

I want to try taking the weights of old pieces and substituting more modern guns of the same weight. Here is a proposal:

Old gun             Wt          New gun   Wt
110pdr Armstrong BL 4 tons      5in/51    4 tons
 40pdr Armstrong BL 1.5 tons    4in/40    1.5 tons
 20pdr Armstrong BL 0.5 tons    57mm      0.5 tons
9in SB Somerset     6.25 tons   5.5in/50  6.5 tons
10.5in Woolwich    12 tons      7.6in/40 12.5 tons
13in Armstrong     22.5 tons    9.4in/40 22.75 tons
1864 6.3in 64cwt    3.2 tons    5in/40    3.1 tons
1864 6.6in 71cwt    3.55 tons   4.7in/50  3.7 tons
1865 7in            6.5 tons    5.5in/50  6.5 tons
1866 8in            9 tons      6.5in/45  9.0 tons
1865 9in           12 tons      7.6in/40 12.5 tons
1868 10in          18 tons      8in/40   18.1 tons
1867 11in          25 tons      9.4in/50 24 tons
1870 12in          25 tons      9.2in/40 24.338 tons
1871 12in          35 tons     10in/40   34.6 tons
1875 12.5in        38 tons     10.8in/45 35.5 tons
1878 16in          80 tons     13.5in/45 80 tons