It's most likely your sear and/or hammer. Check your sear to see if its rounded at the edge where it makes contact with the hammer, if so it needs to be replaced, and check the hammer where the sear rest's. The hammer should have a 90 deg. cut, if its worn it could look like a 70 deg. cut. Use a file to get it back to 90 deg. It should work for a little longer, but will also need to be replace in the near future. Good luck.
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O.P.S. Ottawa Paintball Supplies
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Bells Corners, ON.