You will likely find that the relative recoil spring strength has little to do with keeping the slide closed DURING ACTUAL firing suppressed or unsuppressed. The key is that the suppressor is specially intended, developed for and compatible with your specific model pistol. If it is not properly designed and "tuned" it will adversely effect function and can/will cause serious damage to the frame locking inserts, barrel hood, slide and recoil spring guide rod. I have seen serious damage to USP45T's after less then 24 rounds fired because non-compatible cans were used. Check with and if possible get it in writing from the can maker that your can will work properly on that model pistol, and best case is covered by a warranty. That would save a lot of aggravation down stream.
USP45T's in tests at HK ran for 18,000 rounds without incident with the purpose-built KAC can before any issues arose and that was slight peening on the leading tip of the recoil spring guide rod (easily stones off) and a lame recoil spring. A new stock recoil spring was installed and the gun shot flawlessly to 24,000 rounds and the end of the test. A stronger spring would not have made a difference and it fact can upset the "balance" in an otherwise pretty complex "ballet" of interacting subsystems (can, pistol locking and counter recoil/buffer system and ammo). Smart designers like those at HK know what they are doing and consider all these factors during kinematic calculations early in the development cycle.
G3Kurz
