In 2006 I was very interested in collecting and tweaking classic Impusles, and one of the more interesting mods I built was a "spool valve conversion" system. It involved removing the hammer from the assembly and installing a 100% balanced valve in its place, then linking it to the bolt.
The mod involved a new valve setup, and a new valve endcap too. I was able to reduce the length of the moving components by using a stationary "plug" in the front endcap, which guided the new valve shaft movement.
To help show how it works, I also made ths quick parts movement animation (.wmv video file).
Here's a quick fullyautomatic video I made. You can audibly hear the change in noice, hense the name of the modification.
(.wmv video)