Hi
I belives the sliding problem on you'r mags can be that they are extended lengthwise on the top.
This extension is often pretty visiable as you can see signs of hammering bullets.
The problem with #8 jams in you 4" gun might be becuse you have a soft magspring in your mag and the 4" gun operates faster than you 8" gun does.
That is just a guess but have a look at it.
Regards HÃ?Â¥kan
http://www.vapensmedjan.com