Randy is correct on his points as well Randall. The "actual reason" is the original 22TCM's bullet was longer and would not fit in a 9mm length magazine for the "Combo" Pistol. This was resolved by using a "shorter" bullet to make the 22TCM 9R the same overall length as the 9mm so they could utilize the same 9mm length magazine. Pictured here : google.com/search?q=22tcm+vs+9mm&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj_-_zdvPTdAhWCwFMKHfxKAi4Q_AUIDigB&biw=1280&bih=618#imgrc=wrERem2PdCPLZM:

the 22TCM9R was mainly made so that ria could offer conversion kit like this one for the GLock 17/22 budsgunshop.com/catalog/product_info.php/products_id/714016073/ARMSCOR+RI+22TCM9R+CONVER+FOR+GLOCK+17

the original 22TCM ammo (buds Item Number: 35274) is slightly longer that the 22TCM 9R the standard can be use in the Factory 22TCM 1911 guns from Armscor which uses a modified 38 super magazine. The 22TCM 9R was made to alloy the 22TCM to be used in 9MM magazines so that armscor could offer conversion kits for 9mm handguns. the ballistics and the case are the same only the bullet length was changed

James G if you get to the OBX you can shoot my TCM it will make you smile

the Ria 22TCM 9mm combos use a modified 38 super mag for both the 9mm and the 22TCM

Randall, the 22TCM 9R uses a slightly shorter (9mm bullet length) so the "22CM/9mm" Combo Pistols can use the same magazines.