Witness marks in upper from BCG cam pin

[nimdabew]

I may as well take the edge of a file and put in a relief to avoid having the parts 'help' each other out as a form of break-in.

Don't do this.

[danpass]

Don't do this.

It's already happening.

But if I take off 0.5-1mm I'll prevent the cam pin from slamming the upper and putting undue stress on the BCG slot, the cam pin of course, potentially the bolt, etc

When I first assembled it all the bolt was pretty snug in the carrier and so I figured that was the cause of the harder-than-the-A2 effort to cycle the bolt but now it seems it was the cam pin striking the upper.

It is better now but only because it has nearly clearanced itself a nice little slot.

[nimdabew]

So you are filing into the anodizing and anodized hardened aluminum of your upper, exposing the softer aluminum below, because you don't want the gun to function as intended?

[danpass]

So you are filing into the anodizing and anodized hardened aluminum of your upper, exposing the softer aluminum below, because you don't want the gun to function as intended?

No. The cam pin has already done that.

[Ridgerunner665]

If it ain't broke, don't fix it...

[nimdabew]

That is really stupid, especially after IG comes in and tells you it is normal. Everyone that knows more about these rifles than you tells you not to monkey **** with it and you are going to go ahead and do it anyways.

It's your rifle I guess.

[danpass]

That is really stupid, especially after IG comes in and tells you it is normal. Everyone that knows more about these rifles than you tells you not to monkey **** with it and you are going to go ahead and do it anyways.

It's your rifle I guess.

I haven't done shit. You on the other hand refuse to accept that the cam pin has ALREADY cut into the upper.

It may be widespread, ie: 'normal', but as a mechanical engineer I would never consider an interference issue such as this to be acceptable practice.

This isn't two rough surfaced parts wearing on each other, such as the bcg rail contact with the upper, this was/is an actual interference.


Your commentary is like saying "don't worry about having M4 cutouts in the barrel extension, eventually enough bullets will smooth out that transition"

(which is unlikely due to material differences, just illustrating a comparison)

[thopkins22]

I haven't done shit. You on the other hand refuse to accept that the cam pin has ALREADY cut into the upper.

It may be widespread, ie: 'normal', but as a mechanical engineer I would never consider an interference issue such as this to be acceptable practice.

This isn't two rough surfaced parts wearing on each other, such as the bcg rail contact with the upper, this was/is an actual interference.


Your commentary is like saying "don't worry about having M4 cutouts in the barrel extension, eventually enough bullets will smooth out that transition"

(which is unlikely due to material differences, just illustrating a comparison)

In my job we buy pieces of equipment costing hundreds of thousands of dollars that do the same thing...that is to say they have initial unpredictable wear. These tools are critical to our safety and the success of projects worth millions of dollars. We determined it doesn't matter, that the tools work as advertised, and we rock on. You should do the same with your rifle.

It's not bad engineering unless it creates a problem. It doesn't create a problem, is normal, and doesn't effect the function of the weapon before it happens, while it's happening, nor after it's finished. Bad engineering would be to take something that works and works well, and start screwing with it to improve it simply because you don't like the way it looks or it makes you uncomfortable without ever actually quantifying how it's bad.

[Blak1508]

Just to give perspective, you buy a shoe that fits your feet but its usually after the shoe is worn for a while that the shoe feels the most comfortable even though the shoe is in my size I do not question why one area seems to get wear marks, or the old glove analogy. I understand your concern but it would seem to make logical sense that parts need to settle in, not all contact points are universal throughout an AR, different builds or completes, parts, different tolerances= different contact points. As long as it runs well and is not a major issue I would just keep on moving. All of my firearms have signs of wear or being broken in after actual usage. My DD shows some of the same marks as yours does.

[danpass]

In my job we buy pieces of equipment costing hundreds of thousands of dollars that do the same thing...that is to say they have initial unpredictable wear. These tools are critical to our safety and the success of projects worth millions of dollars. We determined it doesn't matter, that the tools work as advertised, and we rock on. You should do the same with your rifle.

It's not bad engineering unless it creates a problem. It doesn't create a problem, is normal, and doesn't effect the function of the weapon before it happens, while it's happening, nor after it's finished. Bad engineering would be to take something that works and works well, and start screwing with it to improve it simply because you don't like the way it looks or it makes you uncomfortable without ever actually quantifying how it's bad.

I wouldn't be changing anything.


Consider:

It is only about 200 rounds thru the sytem and it is still contacting the upper based on adding some grease and seeing it wiped away, and a 'step' in effort when pulling on the charging handle, therefore its obvious that it is still clearancing itself (and will do so to a certain point).

I was simply considering taking that eventual additional clearancing, since it is going to happen anyway, to that certain point manually in order to avoid having it done with the cam pin directly. Everything that is connected to the cam pin is participating in the process, I don't like that.