I bought a Lone Wolf .40 barrel for my GLOCK 20. I wanted to have the correct headspace and throat. Only part may have been solved, but more may have been brought to question than answered:
first, I had a helluva time getting my Lee Loadmaster 10MM setup adjusted for the .40. You'd think that might be simple, but no. After getting parts (shellplate, small primer setup) I found the 10MM dies too long to set to .40 dimensions. Fortunately, I had 2 sets of dies, and used one powder thru expander to bell the case mouth. It took some fab work, but turned out OK.
Then, I found that I could not load my cast Lee 175TC bullets anywhere near the COAL listed in the books. The protruding full diameter bullet seemed to hit the rifling too soon, preventing a full slide cycle. I seated the bullets deeper, so only the ogive of the TC bullet protruded. That fixed it, but created another problem. The COAL was a bit too short, so rounds would creep to the front of the mag, and by the end of the mag, the slide would lock open as tho there were no more rounds in the mag, even tho there were plenty.
I can see where I can fix this, if I dedicate mags to .40 Short and Weak.

My question(s)
Have any of you tried a .40 barrel in the GLOCK 20?
What have your results been?
Any particular difficulties you have had to overcome?
Insights on the particular struggles above?

The reason for doing this at all was the plentiful supply of brass in .40. I picked up about a thou at the range the other day. I can prolly go back and do it again after the LEO's practice next time.

Well, I figured out the below. My Lone Wolf barrel was chambered short for what I was loading in the .40S&W. Lone Wolf agreed to lengthen the leade of the barrel to accomodate my max COAL.
It has been shipped, and I expect it early next week. Better go load up some boolits for it now.

I'm planning on getting the Lone Wolf 40 barrel myself.
How did it shoot using factory 40 S&W ammo ?

I don't know how it shoots with factory, I don't have any.
But I got the barrel back. I am disappointed. It appears a .40S&W chambering reamer was driven deeper in the bbl to give the longer leade. Problem with that is, it also cut the chamber deeper. I now have something with a chamber longer than a .40, but shorter than a 10MM.

I had the same problem, Dan Sheppard from LWD was very nice and very helpful. He's eager to make his customers happy. I even sent him some dummy rounds from my home rolled and he tailored the chamber to them since they're mainly hard cast bullets.

The barrel eats everything without issue now.