Wrong. Wrong. Wrong.
That "rep from Lone Wolf" is an idiot and should be fired. 9mm and 10mm Glock magazines have completely different geometry. The Glock 20 and the Glock 17 are not the same frame. Glock 20 and the Glock 17 slides have not the same thickness.
The Lone Wolf conversion of a Glock 20 to 9mm relies on the fact that 9mm and 10mm are only 1mm apart. You just switch the barrel and install an 11-pound recoil spring. That's it. For this conversion, you must +P ammo for "reliable" function. Otherwise, you will get FTFs and FTEs. Since you use 9mm ammunition in a 10mm magazine with a gun that has an extractor/ejector for 10mm, this whole setup is still considered rather unreliable. It works, until it does't when you need it to.
The proper alternative is to use a .40 S&W conversion barrel and load the .40 S&W ammunition in the 10mm magazines. This does work reliably. I have done it, just for fun at the range.
However, I question the motivation for this in the first place. You can get warm 10mm JHP loads for home defense and carry on the street, and hot 10mm hardcast for carry while in the woods. I have a Glock 20, so I know what I am talking about. Here are my 10mm defense ammunition choices:
Link Removed -- warm JHP load at $0.85 per round (+ shipping)
50 rounds of 10mm 200gr. Underwood Hardcast for $39.95 + shipping -- hot hardcast load at $0.80 per round (+ shipping)
For hunting:
50 rounds of 10mm 200gr. Underwood JHP for $38.00 + shipping -- hot JHP load at $0.76 per round (+ shipping)
For practice:
250 rounds of 10mm 180gr. LAX Ammunition FMJ for $93.50 + shipping -- matches warm JHP load at $0.37 per round (+ shipping)
500 rounds of 10mm 180gr. Underwood FMJ for $293.90 + shipping -- roughly matches hot hardcast and JHP load at $0.59 per round (+ shipping)
Note, the 10mm 180gr. Hornady XTP JHP load is hotter than comparable .40S&W loads. It has 17 inches of penetration in a gel block vs. the 13 inches of a .40S&W load.
Note, you can shoot the 10mm 200gr. Underwood Hardcast load through a stock Glock barrel as the bullet is gas checked and does stabilize. There have been reports about the 220 gr. Underwood Hardcast load tumbling and not feeding correctly.
More information about specific 10mm loads can be found here:
10mm Stats (4.6" G20 Stock White drsjr1969 YouTube/ 4.75" EAA Limited Pro and 6" EAA Hunter Green) Gel by Choppinbloc
