I have an old Colt A1 (CH) upper that has a loose aperture when the "L" aperture is up. There is fore and aft wiggle, and no side-to-side play. There is also a little movement on the windage drum. When the close range aperture is up, there is absolutely no play in either the aperature or drum and it is just as solid as any other newer A1 or A2 rear site I have to compare it to.

Any issues with using the L aperture, or should I go ahead and swap the whole site assembly? Hopefully i will get it to the range next weekend to try to zero. I uploaded a YouTube video in case my description wasn't clear. Thanks in advance.

Something is wrong in that windage dial.  I don’t know what, but someone here will.  Mine have never exhibited that kind of play.

It's probably the leaf spring under the aperture.  While you have it all apart replacing that, I'd probably just replace all of the associated parts.  If you are unlucky, the hole in the upper receiver that the screw goes through is ovaled out.  It's more than likely the spring though.

Link here to the part:  Spring

JT

Thanks man. I'm going to order a complete assembly from Amherst and replace the whole assembly. Fingers crossed that the upper itself isn't out of spec.

Shark Arms had a batch of uppers once where the pocket was milled out a little too deep. He was suggesting anyone that bought one to put a shim down before the leaf spring. Not saying that's your problem but something to look into.

Since this only happens when the "L" aperture is flipped up, I would suspect that the problem lies in the aperture itself. Most likely, the aperture's windage screw hole isn't centered, which makes it sit too high when on the "L" setting, raising the aperture off of the leaf spring underneath.

That certainly makes sense, and hoping that is it and not an issue with the upper. When the shorter range aperture is up it locks up very tight, so it makes sense that maybe the specs are off on the other side, and it not being an issue with the spring. Still not sure why the windage drum is set at an angle and not flush with the upper. We'll see what happens when I replace the whole assembly.

It ended up being the leaf spring. It wasn't broken just completely flattened out into the recess in the receiver. I had a hell of a time prying it out with a knife. Once I got it out I went ahead and replaced the whole assembly with the new one from Amherst. Everything locked up tight and functions as it should. Good as new $35 fix with USGI parts. Thanks for the advice!

A new leaf spring will take care of it IMHO.