It was very difficult to push the aperture down while over top of the leaf spring to get the windage screw at the right angle to thread through the sight.

What I do that helps, is set the leaf spring down on a flat surface and tap it a couple of times with a plastic mallet. This compresses the spring a bit and makes it easier to install the aperture and windage screw.

I use this one:
Vaughn mallet made in USA

@556Cliff

Thanks for the tip! As long as there's still enough tension to keep the sight from flipping by itself after the hammer treatment it should be good to go.

There is. A couple light taps is all you need.

Well, I had a "FUN" (read a very difficult and frustrating) experience today attempting to install a new old stock A1 rear sight from Amherst Depot into a Brownells C7 upper receiver.

Here's what ended up happening to the flat spring...





It was near impossible to put enough pressure down on the aperture to get the windage screw to pass through without resistance, but I eventually got it through... Unfortunately, after flipping the sight a couple of times (which was very difficult at first) it felt like it became far too easy and the sight was now loose because the spring had obviously become damaged. So I removed the windage screw and rear sight which basically just fell out now that the flat spring was trashed. However, the spring was hopelessly stuck in it's recess. So I tried using various picks to try and get it unstuck, but none of those methods worked and I had to drill a hole in it to get it out.

So I'm not sure if I'll be sending this upper back to Brownells just yet... I just put in an order for a new Colt flat spring through Brownells and I also put in an order through RRA for one of their flat springs to see if one might fit better than the other and also to see if I might be able to salvage this upper with a different spring.

I got my fingers crossed, but I have low hopes.

I'm not sure if the issue is because the recess for the flat spring isn't deep enough, or if it's because the recess isn't long enough front to back? If someone had an original Colt A1 upper to get measurements from we could get to the bottom of this.

Guess I'll put out the @Brownells and @Brownells_ar15 bat signal here so that they are aware of this issue.

There are two videos on YouTube showing how the A1 sights are installed, and if the process demonstrated in either of them is at all accurate as to how it's supposed to go then something is terribly wrong with these modern manufactured slick side, A1 and C7 uppers.

You can see in the Mrgunsngear video that he doesn't have the flat spring down in it's recess as he's threading the windage screw through, but it shows installed correctly later in the video... So I guess we can discount that one. However, the Brownells video has the flat spring in it's recess during the whole installation and the windage screw easily threaded all the way through with not much effort put into having to compress the flat spring.

My experience mirrors yours nearly the same, I tried to install a Amherst Depot USGI New Old Stock rear sight into a couple different Luth-AR C7 uppers and the rear sight flat spring was totally trashed afterwards. On one receiver the resistance of the rear sight and the flat spring was so great, the sight could not be flipped between the apertures. On 1 attempt I tried to remove some material front to back on the flat spring and another i tried to flatten the spring out more, and neither did a bit of difference.
   
I think your onto something with the brownells video installing the rear sight, when I was attempting to install my rear sight kits, the flat spring was visible in the lower third of the windage screw's bore, and its not visible on the brownells install video. Either the spring pocket isn't cut deep enough or length wise long enough for the spring to properly flatten out the correct way. between the Windham, and Luth-AR receivers I've bought, i've gone through nearly half a dozen bad receivers with critical issues. Really makes me think manufactures today don't know how to machine A1 receivers. Luckily I picked up one of the Fulton Slicksides they put out recently and it checks out great, along with some Del-Ton A2 Receivers that are also well made.

At this point in my frustration in trying finding a C7 that works I will hold out for some NDS Receivers.

Same with the part highlighted in red. Mine have been the same and I don't think that's how it's supposed to be. I've assembled 3 Brownells uppers now (2 A1s and 1 C7) and they were all incredibly difficult on the rear sight install, but the C7 upper was the most difficult of the 3. Could it be the springs? I doubt it as I've had the same issue with new old stock and more modern flat springs, I think they're really all about the same. These uppers are either just not machined properly in the cutout for the flat spring, or the hole for the windage screw is drilled a bit too close to the flat spring cutout.

With the problems being similar between the Brownells uppers and and the Luth-AR uppers I'm betting they are getting them from the same source.

At this point, I believe I'll be contacting Brownells and returning at least 4 receivers and that just really sucks, because other than this issue with the rear sights the uppers are really nice. Plus I'm not sure when or if any 100% properly made A1/C7 receivers will ever be made again.

Of the 3 I put together, an old Colt, a Luth C7 and Brownells A1, the only one I did not have this same issue on was the Colt.

Well, that settles it really... That indicates that there is indeed a problem with these new manufactured slick side/A1/C7 uppers.

I took some measurements of the possibly offending areas with my cheap digital calipers of the 4 Brownells uppers I have, but given the cheap calipers I'm not sure how accurate these measurements are.


All the measurements were similar between all 4 uppers...

Length (front to back) of the flat spring recess = 0.625-ish

Depth of the flat spring recess = 0.135-ish

And depth from the bottom of the flat spring recess to the bottom edge of the windage screw hole (this was on left side only with the bigger hole) = 0.090-ish


Now we just need someone to compare these numbers to a real problem free Colt A1 upper.

Maybe @mike_nds could shed some light here?

Did you try the mallet trick? Put the leaf spring on a flat surface and tap it 2-3 times with the plastic mallet. You just need to take a little bit of tension out of that spring by compressing it some. After you thread the windage screw through the aperture, press down on the top of the aperture with a Delrin/plastic punch (to compress leaf spring) as you finish screwing it through the other side of the receiver. Sometimes, you need to press down with the punch and tap the head of the windage screw with the mallet to get it through the other side of the receiver.

I've encountered this issue on about a dozen or so Luth A1 receivers.

On this last Brownells C7 upper that I was having major issues with I didn't attempt the plastic faced mallet trick, but I was getting frustrated enough just before I managed to get the screw through that I was considering it.

I was depressing the aperture with a nylon punch, it was the only way to do it so as not to leave any marks.

In the end on this particular C7 upper I'm not sure that the mallet trick would have helped, since by the time the leaf spring was compressed enough to allow the windage screw to just barely pass that I'm sure the spring was already helplessly wedged stuck in it's recess. So if I had flattened it out enough with the mallet the spring probably wouldn't have fit into the recess anymore.

And I still can't say for certain that there isn't some variance between the flat springs. The measurements on all my 4 uppers were similar, but the 2 rear sights I installed in Brownells A1 uppers previously (though difficult) weren't as difficult as on this C7 upper.

I see. Might be worth while to get a few more of the flat springs to have on hand. They are cheap

https://pkfirearms.com/a1-rear-sight-flat-spring-item-13

Roger that.

I have flat springs from Colt and RRA on the way. I'm going to compare them to the flat springs that came with the A1 sights that I got from Amherst Depot to see if there's any differences between them.

My leaf spring was from Luth. Extremely stiff but it worked.

I checked Luth's site before I ordered my 2 replacements, but the flat springs were only available in their A1 sight kits. Which was odd because they had every other part available separately.

Alright, I got a new Colt flat spring from Brownells and a new RRA flat spring.

Left to right...

RRA, Colt from Amherst Depot, used Colt from Specialized Armament and Colt from Brownells.



The three Colt flat springs appear to have a phosphate finish while the RRA flat spring appears to possibly have a black oxide finish.

I got measurements from all of them except the used Colt flat spring from Specialized Armament since it was somewhat flattened and out of whack. Also, You may notice that the new Colt flat spring from Brownells (far right) is cut differently as it's meant to work more with the recess in the Colt A4 carry handles which is off center, however, it is backwards compatible and fits the flat spring recess in the A1 uppers and I assume the A2 flat spring recess as well.

RRA flat spring: Length 0.580 Height 0.120

Colt from Amherst Depot:  Length 0.598 Height 0.114

Colt from Brownells: Length 0.584 Height 0.116

So a big part of the problem is the length of the old Colt flat springs that come in Amherst's NOS A1 rear sight kits... Combine that with the out of spec recess on these modern A1/C7 uppers and it's an absolute bitch to install these rear sights. Good news is that it's very easy to pre-compress these flat springs with just finger or thumb pressure straight down with the flat spring on a flat surface (such as your work bench). You don't need to use a mallet on them.

Though the flat springs that come in the Amherst Depot sight kits are too long and should be avoided in favor of the shorter length flat springs because there's just not enough room for them to properly compress in these out of spec modern A1/C7 uppers.

Edit: I'll mention that the new Colt flat spring from Brownells (on the far right) was the strongest of the flat springs pictured, but you can get them all to take a significant enough set just by compressing them with thumb pressure alone. I'd recommend compressing them until the top of the flat spring is about even with the bottom edge of the windage screw hole on the left side of the receiver... That should be a good starting place at least.

my spring had two together till i rubbed them between my fingers. Was hard to put in but Im guessing that may be the problem some are seeing. Mine is on a Non FA upper I ordered 2 weeks ago. Ordered a flash hider from brownells . Its a 10.5 barrel which I know isnt correct but its what I can afford to put together right now .

I don't know if this will help, but for those that haven't mounted but want to mount an ARMS #16A Aimpoint mount, my C7 needed to be shimmed with aluminum foil to get it to fit without any wobble.