Not too far into the initial test carve the bit and collet ejected from the spindel. The collet is spread out much wider than it was from the package. Poking around the internet a little I think my mistake was letting that collar sit directly on the collet. This is supported by some frayed/shaved material off of the bit collar.
Hopefully that is the issue, but any confirmation or alternative culprits would be appreciated!
How far into the Dewalt 611’s collet did you have the adapter? When you have it in right the adapter is fully inside the the 611’s collet and rubber ring on the bit should pretty much touch the 611’s collet.
Not using the wrench was 100% the mistake, you cannot get it tight enough by hand. It allowed the adapter and bit slide out. You need to get it snug with the wrench but not so tight you can’t turn it anymore.
Also, I have assumed that you are supposed to insert the bit until the rubber collar touches, and have had no problems with that.
Edit: If you had overtightened it as @AlAmantea suggested, the collet itself would have ejected, not just the adapter. Try fully unscrewing the collet nut and examining how its set up and you’ll see what I mean.
I have bought several bits from Drillman on eBay, but to be honest I usually just search for the type of bit I need and then buy the least expensive one that meets my needs. I do usually buy carbide bits so they are a little more expensive than steel but they will last much longer. Unless I am buying a very small bit (like 1/16 or smaller) then I just get the very cheapest I can find since I will most likely break it before it even come close to wearing out.
Find yourself a nice carbide 6mm shank tapered ball nose, Good carbide 6mm upcut and down cut end mills a 6mm and 4mm ball nose, a 30, 60 and 90 deg vbit (much cheaper with 6mm shanks), a few carbide 4mm end mills. I have never had any trouble no matter who I purchase from. Sometimes it may take 8 to 12 weeks to arrive (some arrive in 2 weeks) but they are always exactly what was advertised.
Just be sure you know exactly what you are buying, read the full description and be sure they specify the shank size and the material the tool is made of. Always be sure you understand the length of the tool, sometimes they will specify the cutting length and sometimes the full length. Lastly know how many flutes and if it is spiral or straight flute each has it uses depending on what you are cutting.