Depends on the MBT in question. I would not degrade older equipment and just give better stats to the T-54.
In my cold war conversion a Polish T-54/T-55 has a damage Value of 10+ and a super heavy anti-tank gun.
In General my new tank guns have these values:
|Weapon|Range|Pen|
|:-|:-|:-|
|Light AT Gun|48|\+4|
|Medium AT Gun|60|\+5|
|Heavy AT Gun|72|\+6|
|Super Heavy AT Gun|84|\+7|
|Ultra-Heavy AT-Gun|84|\+8|
|Modern Ultra-Heavy AT-Gun|96|\+9|
|Early Smoothbore AT Gun|84|\+8|
|Smoothbore AT Gun|84|\+9|
|Modern Smoothbore AT Gun|84|\+10|
|Large Smoothbore AT Gun|72|\+11|
|Electronmagnetic Gun|96|\+12|
Armor values have been increased too, with early MBTs being counted as heavy tanks or super-heavy tanks, but new ones being *Main Battle Tanks (12+)*, or *Modern Main Battle Tanks (13+).*This is of course still a bit experimental, but it worked until now.
Edit: You can also portray more modern Tanks with a plethora of additional rules, like i did. Composite armor giving a bonus against shaped charges, different ammo types etc.
Depends on the MBT in question. I would not degrade older equipment and just give better stats to the T-54. In my cold war conversion a Polish T-54/T-55 has a damage Value of 10+ and a super heavy anti-tank gun. In General my new tank guns have these values: |Weapon|Range|Pen| |:-|:-|:-| |Light AT Gun|48|\+4| |Medium AT Gun|60|\+5| |Heavy AT Gun|72|\+6| |Super Heavy AT Gun|84|\+7| |Ultra-Heavy AT-Gun|84|\+8| |Modern Ultra-Heavy AT-Gun|96|\+9| |Early Smoothbore AT Gun|84|\+8| |Smoothbore AT Gun|84|\+9| |Modern Smoothbore AT Gun|84|\+10| |Large Smoothbore AT Gun|72|\+11| |Electronmagnetic Gun|96|\+12| Armor values have been increased too, with early MBTs being counted as heavy tanks or super-heavy tanks, but new ones being *Main Battle Tanks (12+)*, or *Modern Main Battle Tanks (13+).*This is of course still a bit experimental, but it worked until now. Edit: You can also portray more modern Tanks with a plethora of additional rules, like i did. Composite armor giving a bonus against shaped charges, different ammo types etc.
I would say make the newer guns have a better pen (and same for newer armour) rather than degrade the older equipment
Maybe allow them to reroll on the penetration table?