Topic: Is there a name for this type of breechface?

[Shandra Lynch]

Good Morning All!
The 1st picture is from the breechface of an Inland M2 30 Carbine, and the 2nd is a cc.  I don't really think that the BF marks are circular or arches. They are almost like a fan or pinwheel.  What do you call these types of BF marks? Is there a category for them? Thanks much!

[Mike Beddow]

Overlapping milling marks.

[Shandra Lynch]

Thanks much. I am looking for more of a descriptor, like granular, linear, circular, arches, etc.  Is overlapping milling marks how you describe them in your notes?

[Mike Beddow]

Yes that is how I document them in my notes.

[Shandra Lynch]

Ok. Thank you.

[Nancy McCombs]

Shandra, you would also not be incorrect if you called them arced BF marks, or overlapping arched BF marks.

[Shandra Lynch]

Thank you, Nancy

[Chris Monturo]

I would sway away from arched as they are traditionally associated with Beretta/Taurus 92/96 series where there is clearly a one way arch from the face milling process.  If someone told me "arched" I would think Beretta/Taurus 92/96 style.
While what you have shown does have arches, it is a result of a different process.   Beretta/Taurus is a one time swipe in an upward motion.  What you have is an endmill used in conjunction with a rotation of the bolt face.  This is similar to the Ruger AR-15 bolt face (pictured below).  Overlapping endmill marks as Mark mentioned.

As for a one or two word term to encompass the situation....that may take some time to figure out.  If you want a description, I would classify it as a breechface produced by an undersized endmill to produce the case head pocket (or overlapping endmill marks). 

Not sure if that was much help because I didn't come up with a term, but it gives you the jist of what you are seeing.(edited to say that overlapping endmill marks pretty much sums it up the more I think about it)

Regards,Chris

[Shandra Lynch]

Thanks, Chris.

[Adam Grooms]

It would be curious to know what NIBIN is classifying this BF as?  Maybe AFTE glossary committee can help define a standard term (ie. OE - overlap endmill)

[Charles Clow]

For NIBIN I'd likely say cross-hatched since you have overlapping marks that are not exactly perpendicular to each other but I think it describes the appearance generally.


CMC

[Bob Kennington]

Good Morning All!
The 1st picture is from the breechface of an Inland M2 30 Carbine, and the 2nd is a cc.  I don't really think that the BF marks are circular or arches. They are almost like a fan or pinwheel.  What do you call these types of BF marks? Is there a category for them? Thanks much!

I like pinwheel or "swirl"


Message Bob Hart--he's really good at this. (And many of his terms appear in the Matrix texts).

[Sean Daniel]

At first glance it reminds me of a spirograph


I like the name overlapping milling marks too. Seems to be the simplest term to call it what it is

[Emily Bagwell]

One more vote for overlapping arches over here.

[Christi Bonar]

Chris and Mike,


Without using the machining method, what would your description be?