looks like JSAR has a few m-rod aluminum tubes ,

The aluminum tubes legitimately take 1.5lbs off the gun. That said, the one I had was a teensy bit oversized and I really had to work to get the o-rings to seal up right. I found out it helped a lot to use as little silicon lube as possible on them. Come to think of it, maybe it wasn't the size so much as my never had worked with an aluminum tube before. Don't really know.