Took my new to me 4566TSW out to the range and it performed quite admirably. I was able to shoot ragged holes with it and it was 100% reliable - with OEM mags. I'd heard Promags are garbage, but I bought a 10-round extended one since as far as I'm aware S&W never made extended mags for the 45 guns. I'd noticed that the magazine would not lock the slide back reliably, and once I actually took it to the range I noticed several stovepipes with it while the OEM mags I had performed flawlessly, which is enough firsthand confirmation to me that Promags are indeed garbage. I have read anecdotes of people managing to get their standard capacity Promags reliable enough swapping in OEM followers and springs, but the springs are probably not going to be an option here. Has experimented with using other springs in a 10-round 4506 Promag? For example I know that some people were able to remedy the troublesome 14-round extended mags on Sig P227s by using 14-round Wolff Para-Ordnance springs.