Those individual spring testers are nice but one of the things I usually like to see is what affect the mainspring has working with the recoil spring, which has to been done assembled.
My example above didn't include anything like that (only a standard power mainspring with various recoil springs) but sometimes by increasing the hammer/mainspring a few pounds you can get the extra resistance you're looking for & adjust the recoil poundage accordingly, if wanted.
You might go down a few pounds on the mainspring & then offset it by going up a couple on the recoil, or vice versa.
The chart below shows a comparison of a standard power mainspring & an extra power mainspring when used with the same recoil spring.
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