I don't know if it's common knowledge or not, but I just received my Gamms follower and spring from Henning and iI can squeeze in FIFTEEN rounds with the stock baseplate! Haven't taken it to the range yet but it cycles by racking the slide just fine. I'm stoked! I will probably get an extended baseplate for my backup mags and use the 15 + 1 for concealed carry in a shoulder rig. ;D
I have no issues in my Witness steel full size loading 15 with the stock baseplate. My mags are the older red-follower mags, which apparently are the cause of much problems for many people. I run Wolff +10% springs in my mags and a 22-24lb recoil spring. I also keep my mags loaded all the time. If I let one sit around empty and load it at the range, I sometimes had issues.
Many guns will hand cycle just fine but not shoot. Things happen much faster, and sometimes that means issues.
My K-10 mags have been eating Underwood 180 grain fmj and hollowpoints and 200 grain hollowpoints flawlessly so far. I'm running a Sprinco unit and an 18 lb. recoil spring. I bought the Gramms kit with the intention of getting an extended baseplate for a true high capacity 10mm. I didn't expect the 1 round increase with the stock baseplate. I'll let you all know how it functions, probably next week, but I don't expect any problems since the stock K-10 works fine without any heavier mag springs.
Don't know if any red follower mags can be found and frankly I was scared off of them with the problems reported, so I never looked. If the Gramms works well with the original baseplate and the extended, I will be super happy.