I bought a Crosman Optimus .177 a few months ago. My grandson and I were using it a few times, so there was no heavy use at all. Just a few days ago I tried it and noticed that it has lost considerable amount of power. I took it apart and found nothing significant. No broken spring, no scratches inside the cylinder, seemed to have plenty of lubrication and the piston seal looked fine. I noticed though, that the piston did not move in the cylinder as freely as I thought it should. Also, I did not see any vent hole that is commonly used to limit air pressure. Is it then possible that Crosman is using a combination of seal and lubricant to de-tune the gun? If not, what might cause the loss of power I am seeing with this relatively new gun? The power loss happened over a long weekend.

Thanks for any advice/opinion you might offer.