Yesterday was the last day for my PTTs validity so I decided to hit the range and also get to test the stiffer spring I installed on my HS40. Got 200 rounds. First 100 rounds was ok, Was working on the doubles taps - no problems what so ever. I liked the way the stiffer spring works, recoil wasnt that much compared to the stock spring. I got 60-50 rounds left and everything was still ok. Loaded my mags up and I noticed on my last round, my slide didn't go into that mode where it slides back ( ano ba tawag dun? ). So I checked if something was missing or if it was broke. Put 8 rounds on the mag, did double taps and it did the same thing. So I put my stock spring back, another 8 rounds on the mag and double tapped again. This time the slide went on that empty chamber mode. So I put back the stiffer spring back, emptied the mag and this time it didn't slide back to the empty mode. Replaced the stiffer spring with the stock one just to troubleshoot it. I emptied another 8 rounds, this time the slide didn't go to that empty mode. Racked the slide a couple of times and emptied another 8, this time it went to that empty mode. Now the whole problem was a hit and miss thing. Since I was in a hurry, I fired my remaining rounds with my stock spring. Can't recall if it had that problem again. When I got home, I took out the slide and cleaned the whole thing. I know lead is cheaper but I'm really about to give up on it. Its damn messy when cleaning your gun + the health hazards about it. So was it the gun or some kind of lead build-up?