What should I use to space/shim rail for proper alignment?

[Zzan]

I recently purchased a Madbull Daniel Defense 12" RISII system, the issue I am having is the rail on my G&P upper extends a little too far and causes the RIS to angle down slightly when secured.  Is there something that can be used as a shim behind the ring so that I can push the RIS ~1mm to 1.5mm away from the receiver so that I can get the rails straight and level?

[Stinger]

Apr 7, 2015 10:23:45 GMT -5 Zzan said:

Is there something that can be used as a shim behind the ring so that I can push the RIS ~1mm to 1.5mm away from the receiver so that I can get the rails straight and level?

I think that a properly sized O-ring would do the job just fine.

[Gabriel]

I would suggest sanding to size. I had a similar problem. The only issue is that the upper might not work as well for other rails after.

[Deuce]

I don't know if this would necessarily help, but I've had to wrap the upper receiver's threading in electrical tape so my rail sat tighter on the threading. The point is to make the threading thicker so the rail sits more stable on the receiver, without making the threads too thick that it bunches up. Like I said, no idea if it helps, but it's helped me before.

[Zzan]

I actually cut up a medium guitar pick to make a shim. works perfect. Thanks for the responses everyone.

[T6e9a]

There are such things as barrel shims. Thin metal rings that fit underneath the delta ring and around the barrel. They don't allow the delta ring to be secured as far on. If te gap is too big, I've been know to cut like 1.5" of wire, wrap it around, and that worked just fine, even had a little bit of give to allow for cranking it on, but not damaging any threading.