NMexJim
Member
If this Glock 42 is a blow-back action, then CFE Pistol may be too "slow" to run efficiently. Typically blow-back actions like powder burn rates starting at Winchester 231 and those faster. Consult several Burn Rate Charts if this is new information to you.
While CFE Pistol will allow you to build workable cartridges, you'll may have a lot of black, sooty, unburned powder left in the receiver as proof of what I'm saying.
Please do not confuse CFE Pistol with CFE 223 (111 on the burn chart). CFE Pistol is pretty fast actually at like #44 on the burn chart. Sure, there are faster powders, but it's fast enough. A good all-around pistol powder. It's a flatten spherical powder and is maybe safer for a noob than, say, Accurate #2 or Bullseye or Titegroup.
Ironwill, with a min of 3.3 and a max of 4.0 grains, you're at about halfway, and I'd guess fps at maybe 850? Look up the data on Hodgdon please and double-check me. It should work fine if your reloading technique is good. I have no experience with X-Tream RNFP and can't comment on the OAL. They do have an electronic reloading manual available for $4.99 which would be a good idea IMHO.