Reporting back:
Results were mixed and varied upon ammunition.
My P10F will normally run Federal AE9FP 147 grain ammunition. With the MBX spring and follower, the magazine would not load from an open slide (AE9FP). The round tip would nose down and jam into the feed ramp. If you loaded the weapon from a separate magazine and inserted the MBX equipped magazine (loaded to 24 rounds), generally, the magazine would hang on the feed ramp on the 3rd or 4th round.
Next I tried my loads. The projectile is a Precision Delta 124 gr FMJ V2 loaded to +/- 1.125". Initially, I had some of the same issue noted above. Out of 4 mags, I was about 50% reliable.
I then tried some PMC 115gr RN. No issues running a full 24+1 for (50 rounds or 2 mags).
I then went back and ran my PD JHP loads and made it through a couple of magazines without issues.
When I again tried to run the AE9FP, I had a malfunction in the middle of one magazine and on the 3rd or 4th round on the second.
Basically, I ran out of ammunition and time. At this point I cannot say one way or another if a few more compression cycles of the spring will help even things out. If you run FMJ RN, you may have good luck. I'll be trying more of my PD FMJ V2 today.
I've been running Grams springs and followers in my CZ 75 based magazines for a while now with great success. I don't have the same confidence with these.
The good thing is the Henning's baseplate is compatible with the factory spring and follower out of the factory 21-round magazines. At least that gives a reliable 140mm option. Supposedly you can file down the legs on the factory follower to allow for 22-rounds. For a C-class dope like me, its enough to have fun.
On another note, the P10 has a rather steep feed ramp. One of the reasons I started playing with this is because I've been eyeballing a DWX but don't want to drop that amount of money on something that I cannot feed with competition oriented magazines. The DWX may have a less steep ramp angle that would be more tolerant of the MBX spring and follower.
A.