Chamfer on Ejector Hole - Colt 6920?

[bush-hog]

Just noticed that the edge of the ejector hole on the bolt face of my 6920 bolt is chamfered.

When cleaning it last, I noticed a 'dark' area around the ejector where it protrudes through the bolt face, and thought it might be chipped. Took a high res pic of it so I could zoom in and it definitely has a machined chamfer.

Checked my older AR's (including an older 6920) and the edge of the ejector hole @ the bolt face is not relieved like this - they are simple through hole cuts.

Is this something Colt started doing as a mod in more recent production? Never seen this before.

Thanks in advance.

[bush-hog]

Probably a worthless thread without a pic. Faint red line points to chamfer on bolt face @ ejector hole. Chamfer goes from about 9 o'clock to 3 o'clock in pic.

http://i1307.photobucket.com/albums/s585/bush-hog/6920BoltBreechFace_zps8f2e033d.jpg

[Displaced Texan]

Just checked my Colts, and they all have the same chamfer cuts.
My earliest production is 6/09.

[bush-hog]

Thanks Tex.

All of mine with simple thu-hole cuts are older than that.

This one (shown in pic) is 2011 production.

Makes me wonder why cut is there? Would almost seem to me to promote fouling buildup in well created by chamfer.....

[Displaced Texan]

Likely a stress relief cut.

[markm]

I have no bolts with that cut. :confused:

Hot ammo will get brass flowing into that thing and be a nightmare for reloaders. :mad:

[DocH]

Just checked the two I picked up in December.Had to put my specs on,but they have it.Older one does not.It's a tiny little thing.
Guess I'll just trust that Colt knows what they'e doing,and keep shooting.

[Displaced Texan]

I doubt it's anything to get worried about. Seems to be a simple relief cut to de-stress that area of the bolt.

[Clint]

I have no bolts with that cut. :confused:

Hot ammo will get brass flowing into that thing and be a nightmare for reloaders. :mad:

^ Most likely this.

A sharp, square edge hole will make false swipes on the brass and increase rotary friction between between the bolt and brass during unlocking.

Slightly breaking the edge will prevent this.

*****

Also, is the bolt face relieved under the case rim instead square?

[sva01]

The bolt in my 6920 has the chamfer. The spare bolt that I got from White Oak Armament does not have the chamfer...

[ChrisCross]

Same as above. I had to look really hard but my 2012 production Colt 6920 has that cut also. I'm no expert but Colt is generally very conservative with changes.... so I'm hoping it's gtg.

I am curious why they did it though. Any experts chime in?