is it machined?

[greg916]

took the stocks off one of my sb2( versa pack, i think it is a sb2) frames and installed them on a sb1. the sb1 is obviously cast, however the sb2 almost looks machined. sb1 is solid in the rear, sb2 is "skeletonized". just curious, this is the first time i have ever removed a butstock.

[trotterlg]

I think they are both cast, just using different methods.  Yes, an SB2 frame is hollow in the rear while an SB1 is not.  I don't know if the older SB2 frames that they will not fit high pressure barrels to are hollow or not.  Larry

[quickdtoo]

Versa Pack frames are SB1, H&R won't fit any other barrels to it, even tho shotgun barrels other than the .410 will fit it, see the Versa Pack sticky in the NEF rimfire forum.

SB2 frames are heat treated investment cast alloy, SB1 frames are just cast, dunno of what, but as you noted, very different in appearance, there are sxs pics in the FAQs.

Tim

[greg916]

i knew about the differences in the "visible" parts of the frame, just surprised me to see the sb2 was hollowed out.

[Ireload2]

The SB1 frames appear to be sand castings. This is about the least expensive casting process since it uses expendable sand moulds.
 I suspect that they are cast from some version of cast iron and are not heat treated.
The SB2 frames are investment cast. Investment castings use different tooling and molds and result in different processes.
The investment casting process can be used for high carbon steels, aluminum, stainless steels, titanium and the various high temperature alloys used in jet engines.
The investment casting mold is usually aluminum. The parts can be much more intricate due to the ability of the aluminum mold to produce undercuts and cavities with slides. The aluminum mould is injected with a wax that forms a wax part. The wax part is attached to a tree (sprue and runner system) along with other wax parts. This tree is dipped into a series of ceramic slurries to build up ceramic shell around the wax.  Once the ceramic shell is dried and hardened it is heated to burn out the wax parts. The cavities are poured full of molten metal while the ceramic mold is hot. Once the metal is cooled the ceramic shell is broken and the parts are removed for machining and finishing.

[RugerNo3]

Since the cast iron receivers are not heat treated, they are cast solid. By casting the steel receivers with a hollow or relieved core process, it enables a more uniform heat treating in a faster time frame. Sound production practices.

[greg916]

RugerNo3, and Ireload2, thanks! knew what sand cast was, had heard of investment cast, but didnt understand it. Makes sense.