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I just purchased recoil springs from wolf.. the set comes with one inner, one outer, and one firing pin spring.
The end unscrews, but is has Loctite on it. Heat will be required on the end that unscrews, once disassembled, reassembly is a little tricky, I use tiny Snap-On electronics needlenose pliers to grip the inner shaft in front of the compressed inner spring to allow the cap to be screwed back on, be very careful to use pliers that do not mar the rod or the spring might drag. and with your third hand apply Loctite to the threaded end before threading the end back on.