Lets see the 7mm cartridges are considered adequate at killing elk. There bullet diameter is .284 and a popular weight is 160 gr. The .270 has a bullet diameter of .277 and you can load a 150 gr premium bullet at a reasonable speed.

.270 has .007 smaller diameter and 10 grains lighter than the average 7mm. It does give up some speed though.

If I only owned a .270 and wanted to hunt elk I wouldn't let it stop me.

I should mention I have never killed an elk. Hopefully that changes this fall. Good Luck.