Originally Posted by outkastmike
and there is what looks like a large round flat rubber? disk in there, as soon as i saw it in the packet i presumed it was a back cap bumper due to it's size.
I believe that would be the LPR adjustment "coin". Since some people get all bent out of shape when their marker gets scratched, that is included so you don't scratch up your LPR when trying to adjust it. I don't believe the stock ram has the ability to contact the back of the ram cap anyhow.
Some people remove their spring and spring guide and then replace that with a cut off bolt to "devolumize" the back of the ram. In essence, devolumizing just reduces the amount of air that needs to fill the back of the ram chamber, and should bump up efficiency a tad. No one has really done testing to see how much efficiency is gained that way. Or at least no one has posted up any of their observations as such. Here's a couple of threads you can read if you want to know how to do it.