Ohhh, and having had many barrels move while gripped with AL.....pads, wire, flatstock and milled rockers.....I will never use AL as a primary gripping surface again.
I've also used CU in these various configurations and am very happy with my latest creation wherein I run tie-wire thru 3/8" chunks of 1/4" copper tubing and after tying it to the jaws I SMASH IT onto the barrel surface. I've used the last set of wires on 7 barrels now and haven't had to replace it (which would entail a cost of 8-11min and approximately $.26)
Speaking of cost....I still have 30-40 70yr-old pennies from my lastest-bestest idea setup (not mine, from Jerry Sharrett) but I just don't have enough hands for Sharrett's method. Man must be an octopus!
LOL
That said, I DO check and while even 1/4" CU wire can move if you're not careful. I've never had pennies nor my newest tubing method move.