My 10mm CCO came sprung with a 22# recoil spring an 21# mainspring. I currently have a 24# RS in it and everything is running smoothly. The 22# was causing the brass from hotter loads to get crunched a bit on the barrel hood on ejection.

I want to minimize frame battering as much as possible, so I will be trying a 25# MS and a 20# RS. There's a good chance that it could operate fine with an 18# RS, but I still need the spring to keep the slide closed long enough for optimal ammo performance. Ammo will be Scottsdale 180 TMJ and Underwood DE GD 180's. I wish I had a 23# MS to try first, but we shall see how this test goes.

Thoughts?

Did you see my Witness test in the ammo section? Will be interesting to see what you get... shame you don't have a Chrony to get numbers there too.

I'll check it out now.

25 lb mainspring + a flat bottom firing pin stop.  Then run a standard CCO recoil spring, which I think is around 20 lbs.

that's exactly the plan!  Hopefully Friday.

Finally got a chance to try the combo two weeks ago.  25# MS and 22# RS and she runs like a top.  Brass ejection is perfect with no brass marks on the port and no case crunching out of the 250 rounds fired.  Have just a few rounds over 2000 through it now and look forward to the next 2000.