Anyone ever grind up their own burgers?

Yep.

will not use store bought ground meat.....too scary, always grind my own, 100% chuck

I made some great weird ones two weeks ago.

Half Ground goat, half ground spicy beef kofta
one of the best burgers we have had.

Topped with the Costco Tzatiki sauce.

nope, no killing for me, usually Sams

Yes. I do equal parts brisket and chuck.

For the brisket, do you trim the fat or grind it into the mix?

Yes an I should do it more often than I do. I could get closer to a 70/30 mixture for doing things with ground meat (not hamburgers specifically) as the main ingredient and drain away the fat when the flavors have melded in the cooking process, and the fat content is no longer needed. The great Julia Child didn't fear the fat of meats or butter in her cooking why do we as a nation do so? The ground beef in the nation is presently almost all 80/20 or leaner.

You should tartare the first one. Trim a bit a bit off each cut for the raw version and roll with it. Some egg yolk, purple onions, Dijon mustard, capers...crustinis...heaven.

I did as a child. My parents had a big heavy cast iron grinder with a crank handle. You attached it to the edge of a table with a C Clamp built into the grinder. When my parents passed away my brother took it. I doubt if they make that type grinder any more.

I have one. Labor intensive, but the end result is unmatched compared to Store Bought.