3-shot limit?

[Zoogster]

In CA there is a three round limit when hunting big game with slugs even though you can have more rounds than that when hunting with a rifle.

Yes.

The capacity depends on the species being hunted.
The trick is "game" mammal or bird.
The limit for shotguns is a 5 round magazine as the statute says no more than 6 (5+1) for some non-game species.
So some non-game species can be taken with a 5 round magazine.

http://californiaoutdoors.wordpress.com/2010/01/28/why-managed-hunting-benefits-deer-herds/

California outdoors Q and A
Ask DFG about hunting, fishing and wildlife conservation

Are target shooters limited to the 3-round max shell capacity?

Question: My friends and I were arguing over whether or not recreational shotgun shooters (skeet/trap) are bound in the same way as game hunters by the 3-round maximum shell capacity restriction. I also cannot find any Fish and Game regulations as to whether this holds true for nongame species (such as coyotes). Only game mammals and birds are listed specifically. (Ken)

Answer: Regulations regarding magazine capacity only apply when “taking” game birds and/or mammals (California Code of Regulations Title 14, sections 311, 353 and 507). The 3-round shell restriction does not apply when using a shotgun to take furbearing or nongame species, or when shooting targets, skeet/trap, sporting clays, etc. (CCR Title 14, sections 465 and 475).

Fish and Game Code section 2010 does limit shotguns to no more than six shells when taking “any bird or mammal” and there are Penal Code sections restricting large capacity firearms. Additional information regarding large capacity firearms is available from the Bureau of Firearms Web site at http://ag.ca.gov/firearms/.

So 2 round shotgun magazine limit for some things, 5 round shotgun magazine limit for others, and 10 round shotgun magazine limit (unless pre-ban magazines) for self defense at your "temporary residence" camp.
Yet you can have the legal 10 round limit for a rifle for most hunting (no limit with pre-ban magazines).

Yes I have always thought it was strange.
Shotguns are more restricted than rifles.

 

[Sunray]

"...Was this a common thing in the 50's - 70's?..." Long before then. The Migratory Bird Acts date from 1913.
You'll note that some U.S. States and Canadian Provinces have decided that the 3 round rule applies for hunting anything. You have to know what your State hunting regs say. It is a hunting thing only though.
"...total restoration...going to re-blue everything..." Don't. It'll drop the value by half. You notice the cracked stock?