So I had bought one of the really early L5 pistols in .357 a couple of years ago.  It ran, sort of.  Lots of failures to return to battery.  It felt like there was almost zero spring force pushing the slide the final 1/4" forward.  I finally emailed MRI about it.  They said they had made some changes since mine was built and emailed me a shipping label to return it to them.  After about a week, I got the gun back with a note explaining what had been done.  They replaced essentially the whole top end, including slide, barrel, recoil assembly, and gas piston.  They had run a couple mags of Magtech 158 gr. ammo through it and said it was good.

And for a while it was.

And then it started choking again.  It seemed to be short-stroking or not completely cycling.  I had also started finding little pieces of copper in the dust cover, beneath the barrel after shooting it.  They looked a lot like copper jacket material. I'm guessing the gas port in front of the chamber was shaving the bullets as they fired, pushing the copper down the gas tube and out when the piston opened.  I would bring the gun to the range, having been thoroughly cleaned, and after a couple mags, I'd pull the barrel and find more copper chunks in and around the recoil springs.  I'm guessing the failures I was having were caused by some copper in the gas tube not allowing enough gas through to cycle the gun.

Here's what I would find after firing a few mags:



So I emailed MRI again, explaining my issue.  I also noted what ammo I had been shooting through it, and that all of it ran fine in my MK-XIX in .357 Mag.

Again, they sent me a shipping label and I sent it off. I even sent in a small bag of the copper chunks.   I got it back again, a week later.  The explanation included said they changed the gas piston and recoil springs and test fired a couple mags and declared it fine.  No mention of anything with the gas port.

So I was a little put off, figuring I'd go shooting and have the same issues.  I brought it out and put maybe 50 rounds through it with no issue.  Today I took it out and put another 60 or 70 rounds through it.  Some of this has been factory ammo, but the majority has been my reloads using Zero JSP bullets and AA#9. I'm happy to report that it has run flawlessly to date.  So having only a little over 150 rounds through the gun, I'm not going to say I'm out of the woods yet, but at this point I would say I'm cautiously optimistic.