Thanks for the update about the mags.
I also think the recoil spring is on the heavy side for 9mm. Although, I certainly can't fault my gun's ability to cycle reliably with it. It seems they use the same part# for the 9 and the .40 guns. Midwest Gunworks has it listed as the same part for both guns.
https://www.midwestgunworks.com/page...prod/251350000
I often leave a new gun at slidelock in the case for a while, and then I usually start out with a few boxes of medium power ammo. My theory is that this allows the recoil spring to take it's "initial set" and gives the gun a chance to wear down some micro-abrasive friction points from the machining processes. I don't know if any of this is actually true, but it's my voodoo superstition anyway.
Perhaps this is why I never experienced any malfunctions with weak ammo?
After several hundred rounds through a new gun, I will usually try my best to induce limp-wrist malfunctions with weak ammo in order to determine the guns threshold for reliability with relation to a compromised grip. My copy seems to cycle no matter how i hold it. It has also cycled 100% for smaller kids and adults without anything like a true 'shooters grip'. The ejection pattern is also quite forceful and perhaps more consistent than any other pistol I've used.
All that said, I do wonder how it would handle and cycle with a recoil spring specifically optimized/designed for 9mm and without regard for use in .40 guns. I think it could be even more well suited to people with low hand strength or poor technique for cycling the slide and administratively locking the slide to the rear.
If S&W would update the mag spring/follower, re-spring the 9mm and beef up the guide rods, increase and extend upward the texture on the side panels of the grip, and perhaps use other spring components somewhat closer to an Apex trigger kit from the factory, I think it would make this pistol really, really hard to pass up once a SCD is available. I know it will never happen, but I think this design could be a truly worthy competitor to the Glock 19 with pretty minimal revision. And in more ways than just budget considerations. They have proven they can build a top-tier quality level pistol for less than $300 retail in the M&P Shield 9mm. I suspect they could easily get the SD9 up to this level of quality/durability/reliability with very minimal effort. It's mostly the magazine and recoil spring assembly that need a slight tweak for optimization in my opinion.