LIKE - when I did a search for Frank Hamer Guns, two of our sites came up on the first page

:
http://thegreatmodel8.remingtonsociety.com/?page_id=434
http://vintagesemiautorifle.proboards.c ... &thread=40
On this blog
http://mred-famous-guns.blogspot.com/ about half way down there are several pictures showing an M8, a hat, and a bar labeled "Clyde's hat, rifle & BAR"

- Clyde's_hat,_rifle_&_BAR.jpg (13.58 KiB) Viewed 4896 times
There are several pictures on the web with pictures of Clyde's "scatter guns" and Bonnie's "whip it" cut-off shotgun - most indicate pictures and details indicate that they were Rem M11.
As you've noted there is no mention of the M8 in the inventory nor does one appear in the pictures of or around the car regarding the "captured arsenal".
That said, I'm not convinced the guns in your picture were B&C's. I'm more inclined to see these as logical lawmens guns. And that after they approached the car that this was a logical "flat spot" where they could lay their long guns, freeing up their hands to confirm no more thread, to wipe off the sweat off their hands, and to be able to TALK!

Though defensive violence will always be “a sad necessity” in the eyes of men of principle, it would be still more unfortunate if wrongdoers should dominate just men. - St. Augustine