On the older feed necks there was a jam point right where the neck oped up to drop in the chamber. A little sanding with a dremel will clear it up.
But, you can get a new feedneck from sp, or we carry parts for the sp-8 also at
www.usmilitarygear.com, that will definately solve the problem.
If you want to try to DIY I got pics I can send you, a before and after.
There has been talk of a mod to make it center feed, But I like being able to look over the top of the gun again, and it really helps my old eyes out.
PM me if you ever need help with it, If I don't have the answer i'll get it real quick.