^^^ Those Spikes barrel nut shims came with the Big A$s Rail when it first came out - don't know if they still do or not, but I'd be that they do still include that.
You clocked your barrel nut and checked it's gas tube position without a shim - the hole had to line up about 45-degrees out from top dead center, before tightening. If I remember that right... Anyways, if it didn't, you added a shim, until you got it right. Once you had it right, at the "pre-tighten" spot, you applied torque and lined it up - perfect torque every time.
I still have some of those shims left over for a 5.56 gun, and I've thought about using them on builds after that... but I just torqued those on and went with it. The shims are good stuff, though. You could have a rifle with high torque on the nut, shim it, and still line up perfectly at lower torque. <thumbsup>