Holy cow, I just realized something! (and yes it involves a video game weapon) This looks like a marksman's rifle in Borderlands in a way.
the mental image of you saying that horrifies me.
Anyways with some determination you can add a spring behind the plunger itself operating essentially as a build in recon powerstock. it doesn't' give quite as much room to do so but gives a nice addition without having to do any structural modification to the gun behind planting the spring the end of the plunger and to the back of the plate to keep it in place as it compresses.