My finished Leinad .45 LC/.410 derringer from Excalibur L.L.c. I purchased a 5/16" x 1-1/4" x .041 spring from a hardware store to replace the missing hammer spring from the kit, I was not happy about that. I had to cut about 1/8" off the spring to get it to properly fit but it performs just like the original that was missing likely would have. I also had to use sandpaper rolled around a Sharpie* marker for the first 1/2" of the chamber because the parkerization was a bit thick in the barrel and was difficult to insert the .410 shell very easily or fully. Over all this was a fun derringer to build and really had no problems with assembling it although the trigger spring in the diagram is drawn backwards as noted in an addendum in the instructions for the trigger spring assembly part of the build.