The new Jim Maccari E9870 mainspring seems like it was made for this gun. The spring guide is .475" and the inside diam. of spring is .480", nice fit. I rounded the square ends of the spring guide.added 2 polished washers with moly grease to reduce spring tourque.only about 1/8" of spacer. Even though this spring is a couple of inches shorter than the stock spring, I didn't add any more spacers. did not want to stress the stock plastic spring guide.It is definately a more robust spring. I could tell by the force I had to exert on my spring compressor. I don't have a chrony, but by the penetration tests I did into a phone book, comparing to my B-3 and RWS 48 . all of my guns are .22 cal. I'd say it's shooting a .22 at around 700 f.p.s.
