I recently switched to helical from a slight offset on a Vapor Blackhawk 4000 arrowand the reason beingI shoot an 85 Grain NAP Thunderhead (fixed broadhead). From my understanding itwill give a better flight. Well I went to shoot them with just field tips and first had to adjust my sights as best as i could because none of them would hit in the same spot?? If they fly like this with field tips then i am afraid what the results will be with the broadhead.

When I shot with the slight offset i could group arrows great especially with field tips. I have a drop away rest and there are no signs on the veins of interference with it. I made sure all the knocks are seated properly. I can not see a reason to spin test, especiallywith field tips. Any suggestions, tips, or information on a helical vein that would cause this? is this normal? any help is TOTALLY appreciated Thanks

I'm not sure what could cause it if you're absolutely sure you're not getting contact. But it's not unusual that you have to retune the bow after changing something about your bow or arrow setup.

Your tip is very light, which means your FOC is low. This is not ideal for stability - especially with broadheads. It could be your arrow spine is way off. We might be able to help if you list your bow and arrow configuration.

Mathews Legacy
27" Draw Length
67 Lbs
NAP Quicktune Dropaway Rest
Vapor Blackhawk 4000 Arrows
85 Grain


Last time I checked the FOC it was 12%.
By putting veins ona differentwaywould that change it?

I'm going with what Arthur is saying on this. When you change how your arrow reacts to traveling through the air you will probably have to adjust your sights a little to correct for the different flight patern. The helical will usually stabilize the arrow more because it spins more. This will change the flight pattern of the arrow.

Are you saying that the arrow will no longer group or that they are just impacting in a different spot?

They no longer will group. I understand I have to resight them in. But they just wont group good enough to get an accurate read of which way I have to move the sight.

You probably figured it out incorrectly. I'm not familiar with your arrow, but if it's the one that weight 9.9 gpi, then your FOC would be around 7.5%. If it's the one that weights 8.4 gpi, then FOC would go up to 8.5%. Either way, very low for a broadhead.

Your arrow is likely very stiff for that light tip. I'd try shooting it with a 125 grain tip and see if that doesn't help with arrow flight. Arrow length is also important, and if your's are shorter than 27", then it will react even stiffer.

Making changes will mean that you have to re-tune your bow. You may or may not have to move anything.

did you buy the arrows factory fletched, do it yourself, or have someone else do them?

I'm starting to wonder if maybe the arrows were not fletched properly and that is causing the problem. Especially if they shot groups before w/ offset.

I had them fletched at the local mathews pro shop. Thats what confuses me. I could group great with them before and now its just frustrating when i shoot.

I am going to go back and re calc the FOC and see what i have. But why would i have to change grains now when they shot great before?? Would changing to a helical change the FOC? If my FOC is bad now then why did they fly good with field tips before?

How could i tell if they were fletched wrong. Anything i particularly should look for?

Change in helical will not change FOC.
All the vanes should be equaly spaced around the arrow. The vanes shouldn't becurved in opposite direction. The distance they are glued from the end of the shaft could be part of it.An arrow spinner would help detect if they are heavy on any 1 spot from too much glue.

Could you take some pictures of the vanes close-up and post them?