Hmm. That seems to be a really customizeable system, but it feels like the secondaries should have some customization too, such as ammo types or attachments. For instance:
SSBR-HP-S2ISR
Hollow Point rounds with a short barrel, I'm assuming 20-25 bullets per magazine, with iron sights.
Attachments are a forward grip for added maneuverability and stability, and a bayonet for stabbing things that get too close. The design is built around short-to mid range combat.
or
SSBR-AP-L26LR
Armor Peircing rounds on a long-barreled rifle with x6 zoom.
Attachments are: a small computer unit on the scope to auto-stabilize while aiming, and a magazine holster on the stock for quick reloads.
or
SSBR-L-M1RMLR
Laser rounds with a medium barrel and reflex sight.
Attachments are a collapsible barrel addition that adds to the length of the barrel when extended (it would take a turn or so to extend it) and a computer unit/screen on the side of the scope with a zoomed-in view (x3).
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Secondaries are that- backup weapons, and shouldn't have that level of customization, but if the main weapons have such great variety the subweapons should hypothetically match, as so:
CSSP(custom Synthetic Systems Pistol) could allow some ammo choices logically, excluding Rocket,Flamethrower,Grenade, and the like
CSSP-SR-B "Ticonderoga"
A pistol that fires sniper rounds. It's inaccurate and only takes 3 bullets in a magazine, but can still hit a target at longer ranges than most pistols. Attached is an extended barrel which helps with accuracy.
CSSP-M-D "Sunday Special"
A revolver model firing magnum rounds. It holds 6 bullets at a time and is lethal at close range and effective at medium range. Attached is an automatic hammer which allows very quick firing.
CSSP-ER-A "Guardian"
A pistol loaded with stun rounds. It holds 2 charges per magazine and is only useful at closer ranges. Attached is a spike coming off the barrel or quick and deadly melee strikes.
That's just my take on it, though, I can see why you'd restrict pistols because it's simpler and balanced.