I shoot some 120 gr. powder coated cast lead truncated cone with W231 out of a glock 19 with 4" barrel.

I've chronographed loads from 3.6 to 4.4 of W231.

4.0 grains has by far the lowest extreme spread and standard deviation, and is the most accurate in my Glock. Those shoot at 997 ft/s with a spread of only 16 ft/s. and standard deviation of 7

The 3.6 grain load was too weak to cycle my slide reliably.

The 4.4 load only got to 1086 ft/s and accuracy went out the window

You would probably get similar performance in your model 39 from your bullets. I think 4.0 grains is a great place to start.

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