I intended to send you this picture earlier.
It is a photo of a cartridge casing fired from my Ruger PC Carbine after I installed your Extra Power Recoil Spring (on the left) and one fired with the factory spring on the right.
When I first got my PC, I was a bit disturbed by how dirty and discolored all the ejected cartridge cases were. I don't care about the old cartridge cases themselves, but I was bothered by how much gas and carbon that was, very evidently, venting through the ejection port. I was concerned that it was going to foul the bolt and extractor and blow dirt deep into the entire recoil system that would cause excess wear and eventually cause reliability problems. The main reason I purchased the new recoil spring was to see if that would help this issue--which it clearly has.
I really wasn't concerned with the recoil at the time I made the purchase. However, the new spring reduced recoil much more than I expected, almost as much as adding the muzzle brake did.
I bring this up in case you would like to incorporate this major benefit in your ad copy about the recoil spring. There are plenty of macho types out there that claim not to care about recoil (especially from a pistol cartridge in a carbine) and may not think that they have any need for the improved spring. It does a lot more than just reduce felt recoil.