I have not tried that barrel but I use to have a G20. Supposedly you just aren't supposed to fire lead bullets through the stock (or any) POLYGONAL rifled barrel. I don't think it is a safety issue but more of a bullet stabilization issue. I have heard of people shooting lead rounds through their stock barrel though and getting decent results. Now your aftermarket barrel will have traditional style rifling, this will work much better with hardcast/ lead bullets. You should get good accuracy. Just so you realize, in order to get any real quietness out of a silencer/surpressor, you will have to have a load that is going under the speed of sound. The speed of sound is different depending on things like air pressure, elevation, etc...
I believe the standard speed of sound is 1050fps. So you would need loads that are going 800-900fps. These loads however would lose performance compared to a full loaded 10mm which I believe is 200grs at 1200-1300fps
