False Weak?

[the rifleman]

I was reconfirming my tune today with a bareshaft and decided to switch from my usual 125 grain tip to a 90 grain field point.  The lighter point began hitting to the left of my point of aim ( I shoot left handed) showing the shaft to be weak.  Being the suspicious person that I am, before cutting the shaft to make it act stiffer, I put on a 125 tip---right down the pike and followed with a 148 tip which also hit where I looked.  Anyone else had similar results?  I had heard of false stiff, but not false weak.
Also I found my bareshafts were hitting below fletched so I moved the nock down from 9/16" to 1/2" and most of the time they hit with the fletched, but every once in a while I would see signs of nock low...  I think with either setting feathers would correct any minor issues which are probably at my end---right?
Thoughts are appreciated.

[dragonheart]

Shooting off the shelf, for most people requires a higher nocking point.  An arrow goes thru paradox and while the lighter point impacted to the left, it might not do that at say 20 yards.  What distance are you shooting?

[the rifleman]

I shot 15, 20, and 30yards.

[YosemiteSam]

Maybe if it's deflecting off the riser.  Short draw it to see if the effect is exaggerated.  When I suspect a false weak, I'll short-draw several shots.  I KNOW the arrow should act stiffer if drawn short but if it starts acting weaker, I know it's a false reading.

Make sure you're collecting enough data points, though.  Anything less than 20 shots with the same trend might just be statistical noise due to variations in your shot form.  I prefer to give things at least 50 shots a day for 2-3 days before declaring anything funky other than my shooting that day.  But a better archer would undoubtedly need less.

[the rifleman]

Thanks John.  Our methods are pretty similar--- i literally sometimes spend days with new shafts, switching tips etc before i cut them.  My form has greatly improved, but i always want to be sure.

[slowbowjoe]

I've had that as a result of the arrow being too stiff, and bouncing off the strike plate (like Yosemite just said).

I can often see the arrow kick on 20yd shots; also often hear it on release.