I realized after checking this that the particular mech I chose doesn't have endo/ferro. The principle is still going to be applied to every other mech, but for the Daishi they are going to have to use the special rule you see below that prevents you from changing which gun is in the arm.
If you read between the lines, they seem to be choosing a way to disallow combinations of large ballistics on Clan mechs.
http://mwomercs.com/...d-construction/
Quote
Engine type.
Standard vs XL.
Engine rating.
Internal structure type.
Standard vs Endo Steel.
The location of any critical slots occupied by the internal structure.
i.e. Instead of freely floating as they do in standard 'Mechs, slots occupied by Endo Steel are assigned specific locations that cannot be changed. (The slots still compact to provide as much continuous free space as possible. Just the location [left arm, etc] is fixed.)
Armor type.
Standard vs Ferro-Fibrous.
The location of any critical slots occupied by the armor.
i.e. Instead of freely floating as they do in standard 'Mechs, slots occupied by Ferro-Fibrous are assigned specific locations that cannot be changed. (The slots still compact to provide as much continuous free space as possible. Just the location [left arm, etc] is fixed.)
Heat sink type.
Single vs Double.
A minimum number of heat sinks (varies per chassis) have specific locations they must occupy and cannot be moved or removed in any way.
Customization involving adding additional heat sinks beyond the minimum number is allowed.
The heat sinks still compact to provide as much continuous free space as possible. Just the location (left arm, etc) is fixed.
Heat sinks cannot be added within the engine unless they are part of the minimum number that is included in the base configuration.
Canon OmniMechs generally place at least the 10 heat sinks required for all 'Mechs as part of the base configuration, but they do not always place enough to fill extra space in engines rated 275 or greater.
Whether MASC is present.
If not present, MASC cannot be added by the player.
If present, MASC cannot be removed by the player.
If present, the location MASC occupies cannot be changed.
Some OmniMechs, as determined by Design, have specific weapons or other pieces of equipment (such as jump jets) as part of their base configuration.
These weapons and equipment can be neither moved nor removed.
In addition to the limitations of the base configuration, the following rules apply when customizing any OmniMech.
If any of the following weapons are equipped in an OmniMech’s arm, any Lower Arm Actuator or Hand Actuator that was present in the base configuration is automatically removed:
Any Gauss rifle.
Any autocannon.
Any PPC.
Edited by Praslek2, 07 February 2014 - 04:43 AM.