I do a weekly 3-D shoot at the local archery range. I just started this about two weeks ago and I thought that I would save my expensive FMJ's and opt to shoot a less expensive arrow. I switched to Easton carbon storms and shot groups increased dramatically.

What would cause this? Is my form just getting sloppy or could it be the actual arrow?

I Shoot a Monster 7.0 at 62lbs and a 28in DL. The spine on both arrows are 400's

My guess is it is still a spine difference issue.

Even though the static spine for both shafts is identical. The dynamic spine is most likely different. The actual weight of the arrow comes into play when the arrow is actually fired. The heavier of the two arrows will act less spined because it is under a higher load when released.

You can get equal performance by making slight adjustments in draw weight or let off percentage(if your bow allows).

I will try backing down the weight, thanks!

Just adjust a quarter turn down at a time. I doubt it will take a full turn to do it.

Any diameter difference between the 2 arrows?

Gary

The FMJ's were much slimmer. I turned down the poundage about 3 1/2 turns and it shoots great now. Not that big of a deal turning down the weight, just had to sight in again (pain). I don’t care what the manufacturer says, I should have bought 340's

Spend the money and shoot what you do in the field,,,,,Why would you want to shoot a 3d range to improve your skills and disadvantage yourself with different arrows. To me that is like shooting cheap bullets in a rifle to practice and expensive ones in the field. Try and keep everything on any range as close to actual hunting conditions and you will shoot better, your confidence in what you can do will be better and you will not even question yourself under real live hunting conditions. Plus you won't have to resight everytime you go fom hunting to range conditions....