Were you testing Magnus "Snuffers" that came with glue-on adapter already installed?

Magnus "Snuffers" that are purchased without the glue-on adapters are 125 -/+ grain. The adapters, later added to the head, will add 25 - 42 grains, plus the weight of the glue.

Magnus "Snuffers" that come with the glue-on adapter installed have a combined weight of 125 -/+ grains.

If you installed adapters yourself, the weight of the head was most likely greater than 125 grains, and that would account why the broadhead would not impact where a 125 grain field point was impacting. Not because there is an inherent flight problem with the broadhead.

If the head was, in fact, 150-167+ grains in weight, and you were trying to get them to fly well using the same draw-weight, indeed you probably would have to increase the spine of the shaft if you did not wish to dial down the bow's draw-weight.

Therefore, it is important to know which "Snuffer" you tested; the head that came with the adapter installed, or the head without the adapter. If the adapters were installed by you, what was the weight of the adapter?

Before I purchased my "Snuffers" I tested them for flight and I just did not have the same flight problems you have indicated. Then too, I do not try to get my broadheads to group with fieldpoints, being each are different in configuration and will undoubtedly have different flight characteristics.