Comparing the .308 and the .270, I just took a comparable weight bullet, possibly not the most popular and on both picked the remington core-lokt ammunition
.308 150 grain (exact bullet i use to hunt)
Vel. muzzle- 2820Ft/sec 100yds - 2546Ft/sec 200 yds - 2288Ft/se
Energy. muzle- 2648ft-lbs 100yds - 2159ft/lbs 200yds - 1744ft/lbs
Short Range Trajectory
100yds - 0
150yds - -1.2
200yds - -3.9
250yds - -8.2
.270 140 grain
Vel. muzzle- 2925ft/sec 100yds - 2667 ft/sec 200yds - 2424ft/sec
energy muzzle- 2659ft-lbs 100yds - 2211ft-lbs 200yds - 1826ft-lbs
Short Range Trajectory
100yds - +.7
150yds - 0
200yds - -2.0
250yds - -5.5
keep in mind that the zero is different on these comparison, thats just the way remington did it
also that a 140gr. bullet is one of the heavier bullets a .270 will shoot and the .308 will go up to 180gr.
with that being said in this comparison the .270 will travel a little faster, hit a little harder, with flatter trajectory
but I hunt with the .308 150gr. and I love that round, never had any issues, but all my shots have been under 100 yards so far in my life
once again this is the source i used
http://www.remington.com/pages/news-...allistics.aspx
and you can go there and check out some of the other grain weights as well