Try imr7828 in the stw.I get the best accuracy and velocity in my rifles with 7828 and 140gr bullets.

The Chrony is not the most accurate chronograph in the world, you get what you pay for in most things...I had one and didn't much like it...but properly applied it will do good work. Accuracy isn't the most important thing in a chronograph, comparison is...

However, your loads and velocities are not that much out of the ball park...

Something to consider is most many loads are tested in pressure barrels. and others in various barrel lengths...barrels in any caliber can vary up to 100 FPS, there are fast barrels and slow barrels..you can figure on 25 FPS average per inch of barrel (rule of thumb).Based on this use your chronograph as a means to test one load against another...

Shoot 7 shots, take the high and the low out then average your velocity...knowing how to use a chronograph is absolutly necessary for an accurate reading...

I use mine sometimes for determining velocity compared to pressure in loading for double rifles and accuracy is needed to be successful at this....for a bolt gun its much easier.

We all get a little astonished when we chronograph loads....

My guess is the 270 is not quite where it should be, so try some more loads or up that one perhaps...combine you chronograph velocities with your pressure signs...thats a good clue.