Not seeing any hammer springs below 19lbs.
http://forums.brianenos.com/topic/96497-ruger-p89-mainspring-replacement/
"There is a trigger return spring in front of the trigger that is crazy strong, many moons ago I found a seriously lightened version of this spring can help the trigger without any affect on reliability. "
Uh, I thought the mainspring did the return as well. Trigger Bar Plunger Spring???
"Duane, Ruger P85/P89s are designed around milspec's, literally (and specifically, the specifications inherent to the XM9/XM10 DoD/JSSAP trials of the 1980s)-they're designed to chamber and successfully ignite any known commercial and/or military 9mm parabellum round produced, in given military environments (which means that the rounds can be dirty before being chambered, but still must fire and be extracted normally). This translates into a requisite 10-12 lb DA triggerpull with the Ruger OEM mainspring. A knowledgeable Ruger manager/engineer told me that the lightest that he saw the requirement fulfulled with was with a 9 lb triggerpull, but that was regarded as a bit of a fortuitous fluke, and that 10 lbs. was generally considered the lightest possible, with most guns averaging around 11 lbs.
That's the long answer. I don't doubt that a lighter commercial mainspring could work effectively (and with a proportionately lighter triggerpull) with clean, less tough commercial primers (as opposed to some particularly hard-primered Israeli ammunition that someone generously gave me recently, which DID fire successfully out of my OEM spec P89 (but with some problems with a few of the rounds initially when fired from DA, but not in subsequent SA). As an interesting historical sidebar, the Israeli Air Force was one of the few (and perhaps only) military organization to formally issue the P85 as its organizational sidearm/PDW-and I believe that they still do.
Perhaps a relevant criteria for consideration is the smoothness of the triggerpull, as opposed to its specific weight (within reason). My very late production (August 2007) P89 has a very smooth (albeit somewhat heavy)DA triggerpull-very revolver-like, and a crisp SA pull.
In my opinion, the P89 is a bit of an overlooked (and often disparaged) sleeper of a "combat"/duty sidearm. Ergonomics and accuracy have been significantly improved from those of their P85 ancestor, and throughout its production life, Ruger continuously introduced refinments. They are one of the more durable and reliable DA/SA handguns produced (with the DoD/JSSAP trials as their spur), and I've heard on good authority that Ruger did not fail the XM10 trials (it actually, according to my source, passed with flying colors), but the crucial thing was that the Beretta M9/92 did not fail it, which in all liklihood was a logical, if not specific pre-condition for any of the XM10 competitors to have been awarded a DoD contract.
Best, Jon"
