I need to shim my barrel and made a shim from an .004 feeler gauge. I did not permanently fix it to the lug. the barrel is nice and tight now. My question is when I go to make it permanent, do I need to use an .003 shim to account for the JB weld or can I still use the .004? when you use JB weld, do you spread it all over the lug contact points, or use just enough and make it squeeze out?