I have made several doubles and I have not had a problem with it.
Now, if you fire only one barrel and reload, it's wise to ram both ball to be sure, but up to 8 bores, shooting balls, I have not had any problems. I am now working on a double 62 cal bullet gun, and I don't know if it's going to be the same, but I think it will. 750 grain bullets with 140 grain charges. I am building it as a "spec-gun" so I only get time to work on it every now and then. I don't know when I will finish it, but when i do, I will post the results.

S Zihn