Really all that matters here is what 7mm are you referring to?
There are over 20 different chamberings in the 7mm definition (so for any smartassed answerers to get technical after me and say im wrong here) I will only list the most common in todays world.
7mm Remington Mag
7mm Remington Ultra Mag
7mm Remington Short Action Utra Mag
7mm Weatherby Mag
7.62x39(sks and ak47)
The first 8 are widely used today, with the last four still widely used, but are more of a collector gun than one you are going to shoot on a day to day basis.
Now to your Question. The .270 Winchester is a widely used centerfire cartridge for both medium to big game, as well as target and plinking. I do not own one, but I do like them very much as a low recoiling very accurate round. Developed in 1923, the 270 casing is a 30-06 casing that has been necked down making it slightly longer.
Of the chamberings i have listed, the .308 Winchester is for all practical reasons a near identical chambering. The main difference being a slightly larger bullet diameter by .8mm( the 270 is a .277 and the 308 is .308. but for all intents and purposes, factory loads are very similar. Ballistically the muzzle values are +or- 50 both energy and speed. but the .308 retains more at longer distances.
Over all, yes the .270 and the 7.62x51 are nealy the same,
the rest......not so much!
The next closest is the 7x57 Mauser. The mauser chambering has slightly less velocity and energy( about 2-300 feet per second slower and 2-300 ft lbs less energy) but the case is nearer the same size at 5.7 mm longer than the .270.
And 7mm-08 is nearly identical in ballistics, but the case is 12.8 mm shorter.