Raised ridge on AR rifle uppers??

[Dfariswheel]

I've asked elsewhere, so I'll try here:

I've noticed that on almost all AR-15 and AR-10 rifles there's a raised vertical ridge on the upper's locking pin bulge.

It must serve some purpose, since it's present on almost all AR rifles.
What is is??

 

[vzenmn]

I would like to know too.

 

[Ridge_Runner_5]

Perhaps to maintain structural integrity where the bolt retainer moves?

 

[MisterPX]

A leftover from the forging process perhaps.

 

[Kurt+P+]

There's a very small computer chip in there that's GPS capable so the G-Men can keep track of your rifle. LOL! Alright, I made that up. Sorry

 

[davlandrum]

Artistic flair?

 

[Denny Hansen]

It's not on "almost all" it's on all ARs. Viewed from the interior it is a recess to allow space for the cam pin to turn when the bolt is fully forward.

Denny

 

[Dfariswheel]

it is a recess to allow space for the cam pin to turn

We know.
I don't mean the cam pin bulge, I mean the small vertical raised ridge ON the bulge.

No one seems to know what purpose it serves, but it's on almost all AR-15 and AR-10 type rifle uppers.

 

[David the Gnome]

The only functional use I can see for it would be additional structural integrity. Perhaps in the event of some failure it is meant to provide additional support. That's just a guess but it doesn't seem to serve any other purpose.

 

[Denny Hansen]

Sorry Dfariswheel, I read your post too fast. No idea why it's there myself.
(good photo btw)

Denny

 

[Dfariswheel]

After asking around various sources, apparently NO ONE knows what it's for.

 

[B. Lahey]

How are most AR uppers made?

it looks like a remnant from some kind of industrial process. Casting, welding, super-secret Colt fumburkolyzing, something...

 

[CGSteve8718]

Until you asked this question, I didn't even notice the little ridge on mine either.

I can't imagine something seemingly so insignificant can serve any major purpose. I am with the crowd that believes it is a mark left over from the machine/creation process.

 

[TheManHimself]

I believe I read somewhere that it's an indexing mark used in the machining process because the raw forging has no other perfectly vertical lines.

 

[Horseman]

I would certainly vote for an index mark. Being small and thin would help maintain uniformity vs. indexing off a bigger/rounder piece of the reciever.