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Author Topic: Is there a name for this type of breechface?  (Read 1770 times)

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Offline Shandra Lynch

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Is there a name for this type of breechface?
« on: September 13, 2022, 09:41:15 AM »
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!
36712-0
36714-1
« Last Edit: September 13, 2022, 09:44:09 AM by Shandra Lynch »

Online Mike Beddow

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Re: Is there a name for this type of breechface?
« Reply #1 on: September 13, 2022, 12:30:19 PM »
Overlapping milling marks.

Offline Shandra Lynch

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Re: Is there a name for this type of breechface?
« Reply #2 on: September 13, 2022, 12:55:04 PM »
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?

Online Mike Beddow

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Re: Is there a name for this type of breechface?
« Reply #3 on: September 13, 2022, 01:06:28 PM »
Yes that is how I document them in my notes.

Offline Shandra Lynch

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Re: Is there a name for this type of breechface?
« Reply #4 on: September 13, 2022, 01:13:15 PM »
Ok. Thank you.

Offline Nancy McCombs

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Re: Is there a name for this type of breechface?
« Reply #5 on: September 13, 2022, 03:15:11 PM »
Shandra, you would also not be incorrect if you called them arced BF marks, or overlapping arched BF marks.
Nancy D. McCombs
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Offline Shandra Lynch

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Re: Is there a name for this type of breechface?
« Reply #6 on: September 13, 2022, 03:31:12 PM »
Thank you, Nancy

Offline Chris Monturo

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Re: Is there a name for this type of breechface?
« Reply #7 on: September 13, 2022, 07:23:32 PM »
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
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« Last Edit: September 13, 2022, 07:27:52 PM by Chris Monturo »
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Offline Shandra Lynch

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Re: Is there a name for this type of breechface?
« Reply #8 on: September 14, 2022, 09:06:54 AM »
Thanks, Chris.

Offline Adam Grooms

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Re: Is there a name for this type of breechface?
« Reply #9 on: September 14, 2022, 02:43:12 PM »
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)

Offline Charles Clow

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Re: Is there a name for this type of breechface?
« Reply #10 on: September 15, 2022, 09:20:57 AM »
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

Offline Bob Kennington

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Re: Is there a name for this type of breechface?
« Reply #11 on: September 20, 2022, 07:49:20 PM »
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).

Offline Sean Daniel

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Re: Is there a name for this type of breechface?
« Reply #12 on: September 21, 2022, 09:20:43 AM »
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

Offline Emily Bagwell

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Re: Is there a name for this type of breechface?
« Reply #13 on: September 22, 2022, 09:12:09 AM »
One more vote for overlapping arches over here.
Emily Bagwell
Technical Leader
Georgia Bureau of Investigation

Offline Christi Bonar

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Re: Is there a name for this type of breechface?
« Reply #14 on: September 22, 2022, 12:59:13 PM »
Chris and Mike,


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


 

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