Great news! This what Ruby said in another forum, on how to make any gun combination stick ( for example, Infinity Conference Call )
Rubyredsquirt
"The secret is when you are mix and matching partsPUT THEM IN THE BANK lol, If the dont appear in ur backpack try puting them into ur bank. I just made a infinity rocket launcher and a infinity confrence call too. If you guys cant get it to work ill post some codes that im using : )"
So, if you put your weapons in the bank, they will stick
FULL credit to Ruby for finding this out.