Hex bit shank conversion from straight shank to retained

[mbatarga]

I have a set of 7 hex shank bits that are nut driver style. The issue was they are straight shank and fall out of the driver whenever gravity exists.
As I recently got an estate sale purchase of a Craftsman lathe that I've posted on this forum previously

Recent vintage Craftsman Lathe purchase ...

I went to a local estate sale that I saw on the EstateSales.NET app Friday. Lots of "junk" and most of the power/hand tools were older and lower quality than what I usually would purchase. There was a Craftsman metal lathe (Model 101.21200) with lots of tooling that caught my eye - I spent over...

www.garagejournal.com

I thought it would be rather easy to machine a recess in the straight shank and make them retained in the driver. That was a false assumption I've posted a picture below of the machined bits where I've added the cove recess that closely mimics the radius which i measured on existing bits that work.
Anyone have any experience on this conversion (?) - as I can't get any of the 7 bits I've converted to actually be retained fully. I pretty much free handed the modification just based on measuring current working hex shank bits. None of the 7 revised bits worked in a Ridgid driver or in my Snappy hex shank chuck.

 

[KnurledNut]

@mbatarga
Is the round portion of the shank preventing the bit from fully inserting?
Other than that, the machine work is a little crude with tolerances varying greatly. The fit would probably be sloppy even if they did lock in.

I have done several myself, all freehand like this stubby nutsetter.

 

[whateg01]

Second that! Insert one of the factory ones and see how far it goes in. You'll need to turn down the round section to 1/4" or make it a 1/4" hex for that length.

 

[vjquan]

Shouldn't be difficult, it's just a couple of ball bearings locking into two opposite corners of the shank. I modified a hex shank with a round file with no issues. What is not working?