Great products
I ordered different hammer springs for my m9a4. Thoroughly tested them along with optimized hammer. I settled for 13lb for self defense. All worked great. The 12lb had light primer strikes with cheap foreign remanufactured ammo with rock hard primers and nothing else. The other springs were 100 % perfect. I opted for a margin of error so I went with 13. 12 worked great with all US commercial ammo. The trigger pull weight difference was less than 1/2 lb difference in DA between 12 and 13. 13lb pulling between 6.5 and 6.75 DA. SA is about the same at 4.25 lbs. Great products All around from Langdon.