Here's an example of LE thinking in 1976:
6" barrels were awkward for daily hip wear in a cruiser. The 4" was the best compromise for ease of carry and useful sight radius. Adjustable sights had a reputation for snagging on clothing and cutting flesh. Fixed sight guns were also cheaper and the taxpayers were often footing the bill (and when they were not, the individual officer who also had to feed his family was). The .357 Magnum was deemed too powerful and thus politically incorrect in many jurisdictions.
Ruger met the demand with the Police Service Six in .38 Special for markets that prohibited more powerful cartridges, and in .357 for areas that accepted it. They didn't care which caliber they sold, they both cost the same to produce, Ruger was simply interested in major penetration of the lucrative LE market.
However, starting in 1973 after the catalog lineup settled down a bit (references to adjustable sight .38 Special guns were deleted, as were references to 6" fixed sight guns, and the Speed Six was introduced in both calibers but only blue at first), Ruger also made some price adjustments which can only be attributed to their desire to sell to LE. This was the substantial discounting of the .38 Special guns. At this point, the .38 caliber SDA82, SDA84, SS82, and SS84 all carried an MSRP of $91 versus the .357 models SDA32, SDA34, SS32, and SS34 which were MSRP $102. The stainless .38 GF82 and GF84 were $116 versus the .357 GF32 and GF34 at $127. Not because it cost less to make a .38 Special, but because they saw the LE market as the driving force for .38 Special sales and they subsidized that market to gain a foothold.
Starting with the 1974 Distributor price sheet, Ruger proclaimed their intent by adding this footnote below the DA revolver section:
We are anxious to be of special service to Police Departments and Law Enforcement Agencies. Accordingly, we urge our Distributors to indicate "Police Customer" on orders when appropriate. Also Ruger Distributors should not hesitate to contact us in regard to our furnishing double action revolvers with specifiactions other than those listed in our catalog, if the order is for a police agency and is for a substantial quantity.
Then in 1975, coincident with an overall price increase, the price differential between blue .38's and blue .357's increased from $11 to $18 with the .38's priced at $112 versus the .357's at $130. The stainless guns went to $135 for .38 and $149 for .357. Because the sales on the .38 Specials resulted in a loss (or perhaps, more of a loss - WBR was quoted once as saying that the company never made a dime on the entire -Six series DA line), the .38 Special guns starting in 1975 carried an asterisk next to their entries in the price sheets:
* SHIPMENTS RESTRICTED TO ORDERS SPECIFICALLY FOR LAW ENFORCEMENT USE
In 1978, the LE restriction went even further, extending to ALL fixed sight models (Service Six and Speed Six, all calibers, including 9mm in blue at this point). The price differences were more substantial by then with blue .38 FS guns at $118, blue .357 & 9mm FS guns at $140, and blue (.357 only) AS guns at $172.50. Clearly the LE guns were being subsidized by the Security Six. This is the time frame when I first had my lust for a stainless Speed Six and they just could not be found anywhere. And one of the shops I frequented was an LE supply house in Denver, and the shop owner would have sold me one if he got one that was not allocated to LE, but they just didn't show. I finally settled on a blue one but it took a while even to find that, I think it was 1980 before I found the blue gun.
In 1979, the .38 Special subsidy went away. Both calibers in fixed sight guns then sold for $140 in blue, $154 in stainless. The adjustable sight Security Six went for $177.50 in blue and $192 in stainless. But now the Big Grip target (T) models came out and sold for a premium. Ruger must have felt that they had penetrated the LE market well enough at this point that they no longer needed to subsidize the .38 Special (and as more and more agencies began to allow the .357, it became less important to make those .38 sales).
1980 saw an increase in the 9mm guns over the .38 and .357 models. Those were a niche market anyway and maybe the cost increase was justified by the necessary inclusion of the moon clips.
In 1982, Ruger must have seen another opportunity in the Speed Six. It was a popular seller with private citizens as well as LE, so it got a larger price hike than the Service Six, which was still largely targeted toward the LE agencies. From this point throughout the end of production in 1988, the Service Six continued to be offered at a discount to the Speed Six.
The Security Six was dropped in 1985 with the MSRP of a stainless model at $338 (standard grips). The GP100 showed up in 1986 at $340. The GP100 was at first only offered in stainless, .357 Mag, adjustable sights. The fixed sight Police Service Six and Speed Six continued to be offered in both blue and stainless and in both .38 and .357 through 1988. The blue GP100 appeared in 1987. In 1989, the fixed sight GP came out in both .38 and .357 to replace the -Six series fixed sight guns, and the 5 shot SP101 came out that same year in .38 Special only.
In the -Six series, only three models had the staying power to last from 1970 until 1988. Those were the blue, fixed sight, square butt guns, .357 models SDA32, SDA34, and .38 model SDA84. In the 1970-1974 time frame, these were marked as Security Six, but the name changed to Police Service Six in 1975 to cater toward the LE crowd.
So most .38 Special guns were sold to LE and often at the exclusion of even being available to the public due to the discount to capture LE market share. And the Speed Six was not offered in the early years, and not offered in stainless for a couple more years. Then for a several years, the Speed Six was more expensive than the Service Six. The bread and butter duty weapon in Ruger's line up was the SDA84 and later the stainless GF84. Where allowed, the SDA34 and GF34 were sold but at a premium over the .38 for years.
The 4" heavy (H code) barrels came out in 1978 and became all but standard by the mid 1980's and were no longer noted in the later sheets.
The 3" barrels were never cataloged. They appear in the later years but the 2.75" barrel guns were the only snubbies cataloged. All 3" barrel -Six series guns should be thought of as collectible. They are most often seen on Speed Sixes (the U.S. Postal Inspector contract being of this type, and many of the remaining GS33P guns were likely overruns of the GS33PS) but the Service Sixes also sported the 3" tube occasionally. I do not believe that the Security Six exists with a 3" barrel, which came out in 1985 as the Security Six was fading away. But it is possible that a few were made.