Original Vaqueros had steel grip frames and alum alloy ER Housings. About 1/2 way thru their production post c. 1999, steel housings were used.
From my Ruger Tutorial:
Complete blue steel Grip Frame including size vs. alum alloy usage, and steel vs. alum Ejector Rod Housing usage:
Note: Ruger refers to their blue steel grip frames as alloy steel in their catalog, meaning Chrome Molybdenum (Chromoly) as opposed to Alum alloy or stainless steel grip frames.
Blue steel GFs* on the following models:
All New Model Flat Top Blackhawk mid-size and large cylinder frames, and New Vaquero mid-size cylinder frames, XR3 size (also cut for indexing pawl system, no extensions into main frame & only 7/16" thick).
All Super BHs old and new models (exc. Hunter models); XR3-RED size on short brl. lengths; Dragoon size with 7 1/2" & 10" barrels.
All original large frame Vaqueros, XR3-RED size.
All SHORT grip .32 Mag Vaq. style single sixes & 500 .32 Mag Vaq. style single sixes with the XR3-RED size GFs.
Old Army beginning 1985, XR3-RED size.
All Bisley and Birdshead grip frames.
All "Super" Bearcat old models introduced in 1971, have steel frames.
All new model Bearcats introduced in 1993, have steel frames.
Aluminum alloy grip frames on the following models:
All blue single sixes 22 and 32 (except the 32 Mag Vaq. style and Bisley 22s & 32s).
All large size cyl frame NON-flat top Blackhawks, XR3-RED size.
All Old Models, XR3 GF, pre 1963.
All Old Models including Hawkeye, XR3-RED GF, 1963 to 1973 (except Super BH).
Old Army XR3-RED size, pre 1985.
All Old Model Bearcats prior to the Supers have alum alloy frames.
Steel ERH* on the following models:
All pre c. 1962 old models including Bearcats; new model Super BHs since c. 1999 in all barrel lengths (including 5" ERH on 44 & 357 Max 10" barrel).
Late original large frame Vaqueros except post c. 1999.
All New Vaqueros and .32 single six 'Vaqueritos'.
All New Model Flat Top Blackhawks.
Alloy ERH* on the following models:
Guns with alloy grip frames usually have alloy ejector rod housings except early old models which had steel until c. 1962.
Old Model and NM Super BHs post c. 1962 and pre c. 1999.
Original large frame Vaqueros pre c. 1999.
Late old model Bearcats post 1962.
All the "Super" Bearcat old models introduced in 1971, have alum alloy ERHs.
All new model Bearcats introduced in 1993, have alum alloy ERHs.
The early stainless Bearcats have alloy silver anodized ERHs, only recently changed to Stainless ERHs.
*NOTE: There are several dealer exclusive, non-regular production model exceptions to the above such as the Buckeye Blackhawk convertibles that have steel GFs and ERHs, etc.