Deanna, Yes the lower is multi-cal mil-spec lower, but Chiappa has a 22lr conversion also as CMMG as I explained in last response. AR rifles are easy to handle and fun to shoot. The MFOUR-22 captures the best features and attributes of the AR platform but chambered in .22LR. A near identical replica of an M4 carbine, the Chiappa's MFOUR-22 is perfect for inexpensive plinking, practice or for training at ranges where centerfire rifle cartridges are not allowed. MFOUR-22 rifles come with a removable carry handle, flattop Picatinny rail, A2 style front sight post and 16" barrel. MIL-Spec components fit the Chiappa's MFOUR-22, such as grips, two piece handguards and stocks. The MFOUR-22 comes with either two 10 round magazines or two 28 round magazines depending on local laws and regulations.
The MFOUR-22 is also available in a pistol configuration with a 6" barrel or as complete upper receiver conversion that will work on any MIL-Spec AR lower receiver.

Yes the lower is multi-cal mil-spec lower

Deanna, yes Ma'am it is "Multi-Cal" and Mil-Spec to accept different caliber Uppers with no issue.