150 gr - yes
.270 - why? Just stick with the 150 gr 30-06 ammo since that is what the gun was made to fire.....
I believe the .270 round is what the designers wanted it to use in the Garandso they could fit 10 rounds into the clip but the military ordered the rifles in 30.06 do to the massive supply of 30.06 ammo already available for the 1903's. Enjoy that Garand!!