Arrow spine ?

[MCNSC]

Have a question on arrow spine. I am getting erratic arrow flight from one of my bows. I had the same problem with this bow before and had put a Bear Weather rest on it and it shot great. Riser was replaced and I am again trying to get it to shoot off the shelf  as I don’t have another Weather Rest around. Anyway tried from 125 to 200 gr points with no noticeable difference. I built out the side plate and arrow flight improves a lot. ( which helps explain the good flight from the Weather Rest) . Question is is that showing my arrows are too weak? I thought it would make the arrow act weaker , meaning i would need a weaker spine. But reading on the web I’m getting that the opposite is true. Hope that is somewhat clearer than mud. Any insight appreciated.

[Orion]

Yes.  Your arrows were too weak to start, though the heavier heads should shoot a little better than the lighter heads because more weight up front softens the dynamic spine.  Building out the side plate enables a weaker spine. Or, looked at another way, requires a weaker spine.   

[Friend]

Building out the shelf requires the shaft to bend more as it shoots around the shelf.

Just a rough estimate - a 1/16" increase in shelf increases the spine by approximately 5 pounds.

[MCNSC]

Thanks for the replies, looks like I’m going to be needing some stiffer arrows.