It could possibly be that they did strip, if you have used them before the upgrade. The stock sears aren't made of steel so something might have stripped. If you haven't upgraded the trigger assembly, it could be possible that the housing cracked or, though very unlikely, the spring may be too long when compressed for the sear to catch the piston. I'd say take it apart and see what you find out.Today I got a utg tune up kit for my Javelin/Snow Wolf m24. I put the new spring, steel spring guide, and steel piston in my cylinder. After firing one shot I noticed my bolt was not catching when i pulled it back. I was using stock sears but could they honestly strip after one shot? Could it be something else wrong here?