Colt Match HBAR Rear Sight Issue

[Mikee Loxxer]

I have a Colt Match HBAR that I want to use in high power matches. The issue I have is with the rear sight. The rear sight body does not seem to square up with receiver body/carry handle, see picture. What could be done to fix this? I have heard of having the rear sight pinned but am unsure what this means.

 

[M1key]

That's a bit excessive. Try a shim to straighten it out.

M

 

[Mikee Loxxer]

I am not sure what kind of shim to use or how to put it in place.