Hope to test it this week. I did the installation today and want to share what I learned.

In addition to the Hillman #9 springs from Lowes I ordered the McMaster-Carr Part #:9663K13 spring. They were in stock in Atlanta and arrived next day (I have no idea how a Sunday online order can be delivered on a Monday via UPS)

I did 2 tests. The outer diameter of the Hillman #9's rubbed the interior of the bolt. Neither the OEM or McMaster springs did this.

Now how to measure the spring strength? I took my 1000 gram digital scales and did a pressure test by pushing down against the scale tray with the firing pin in the spring until the tip of the firing pin touched the scale plate.

The stock spring was around 12 ounces

The fixed length Hillman #9 was 6 ounces

The cut McMaster was also around 6 ounces.

I thought both springs were too light for my stock hammer, so I cut another McMaster but made it one and a half the length of the OEM spring.

That one measured a little over 9 ounces and the one I'll be testing.