Praise for the FMJ??
I recently had been somewhat discouraged by my lack of grouping from my setup. I was shooting with my buddy who was using FMJ's and he swears by them. I had been buying a lot of arrows off of eBay and generally just looking for a deal. I finally broke down and bought 13 Easton Axis FMJ's and my groups have shrunk CONSIDERABLY.
I also went from a 100 to a 125 gr field tip. The distance from my center shaft to the FOC balance went from 2 7/8" to a hair over 3 1/2". I guess my question is, was the increased field tip weight or the change of shaft the main reason for a vast improvement in accuracy? I guess the only downfall is now I'm shooting a 13 dollar arrow!
Change in Arrows
I don't know what you were using prior to getting the FMJ's.
In addition to you changing your arrow, and increasing your field tip weight, and FOC, you have changed the arrow reaction to the increased weight.
I used The Archery Program and have spent a fair bit of time looking at the result of changing spine, and tip weights. Increasing you tip weight will tend to indicate a weaker spine, compared to a lighter tip weight.
If you were shooting 100gr tips, and changed to 125, you may have moved from a set-up on the stiff side of optimal to and weak side. Everything I have read says it is better to be slightly under spined, then slightly overspined.
As far as I am concerned for myself, I don't think I am good enough yet to notice a drastic difference, at the target end, whether it is a cheap or expensive arrow. I just went from $7.50 arrows to $12.50 arrows, and I didn't notice any difference in groups.
At 10 yards, I usually hit withing 3/4" of the spont, at 20 yards, 1.5", and at 40 yards, within about 3". If I can do that consistently, I will get good kills, if I use good form on a well placed shot.
Another thing, between 100 and 125 tips. With 100 tips, you will shoot faster than with 125 arrows. I did the kinetic energy calculation and it is very close to the same. For hunting, I kicked up my draw weight from about 58 pounds to 70 pounds. My arrrows with 100 tips are going out at 290fps, which make for a much quicker and flatter trajectory.
I was shooting gold tip 5575's before. My total arrow weight should be somewhere around 400 grains and since i only shoot a 25" shaft, its nice to have the FMJ's for a little added weight. So your synopsis would be the heavier tip helped more with my grouping due to "weakening" my arrows spine?
Looks like the spine on the Goldtip 5575's is 0.40. On a short shaft, and tip, I suspect you had a stiff arrow reaction, and adding more weight made it not as bad. So, I believe the heavier tip has helped you.
Be sure to check those FMJ's closely if you have a tight grouping, I have brokenquite a few of them by grouping them too tight. The aluminum will get gouged and break the carbon inside, so make sure to check your arrow straightness from time to time.