OK -I ain't a rocket scientist. I know from years ago, that chain fires were caused by flash hitting the front of adjacent cylinder w/ enough to ignite that charge. YES -a lub wad over powder under ball should keep that from happening. Actually that is their main purpose--the other is to also keep barrel lubed better after firing. As far as promoting accuracy, I am not sure except that it might help compress the powder tighter and the ball seats more closer to the mouth of the chamber with a lesser load. You might want to get some other senior members to comment on that one before I get hung! But I think it is so.
I am now convinced about amco nipples. I hear alot about chain firing coming from the nipples. I have seen Rems throw off caps after a fire. Especially pietta nipples. w/ #11 If the adjacent cap falls or knocked off -yes a fire can explode that chamber. What is so funny--I see these guys use #10,s all the time but they never worked well in my hand. Either I don't seat them properly because they always fire after the second pull. I have seen some caps that are 10.4 size but don't remember the name. Amco supposedly will seat #11's perfectly