I have this one hemmed up. After numbering the mags, I narrowed it down to 2 of the mags that seemed to be causing most of the issues. The spacer in the back of one of the mags fell out on its own volunteering that mag for a 10mm conversion. I went ahead and converted that mag by milling out the dimples and installing a modified white follower. Just for fun, I decided to shoot 40s thru it and the gun functioned flawlessly. So, that gave me the go ahead to convert the 4013 to 10mm.

My Hypothesis, I think the lips on the mag don't grab the round good enough and it only takes a light forward slip for the round to jump out. If it is a 10mm or at least allowed to seat all the way to the back of the mag, it isn't an issue. S&W should have left the spacer out of these mags. I do not think they were needed. Other manufacturers don't put spacers in the mags for a 40 when in a 10mm length mag.

Went ahead and reamed the 4013 barrel to 10mm and converted a 2nd mag and so far, the gun has ran flawless. I have the Wolf 21 lb single spring installed. I also replace the aluminum guide rod with a stainless one.

Now the dilemma is, do I convert the 4053 to 10mm also? Or leave it as 40? Will leave as 40 for the time being.

Rosewood