Been doing some tuning for my new 60" 53@28 John McCullough Griffin with CX Terminator Selects 45/60's. I draw this bow a little over 28". Initially, I shot a FL bare shaft using the stock insert with 235 points. Shaft showed weak at full length so I started trimming a shaft back to where the BOP was 30.2". Overall, the shaft seemed good so I fletched up two. Later I trimmed one of the shafts for a BOP of 29.92". With both these set-ups I was getting good flight and the bow seemed PDQ and shot where I looked.
Today, I decided to start from the beginning and see what happens with these CX Terminator Selects. Took a full length fletched and bare shaft and loaded up the shaft with 50 gr brass insert and 235 gr points (using 160 grain point and 75 grain steel adapters) for a total head weight of 285 grains.
To my surprise both shafts flew extremely well. Both shafts ended up side by side with the bare shaft 2" to the right. Observing this I took my other two cut shafts and loaded them up with the same point weight and brass insert. All I can say is WOW! These arrows with this bow are like a lazer guided missles.
What truly baffles me is when I plug these shafts into Stu's calculator they all show dynamic spines being extremely weak for this Griffin's Dynamic spine of 59.7#. A spread of 15.5#-28.7#.
Here is a breakdown.
FL Shaft 32.874" BOP
612 grains FOC 22.1% 11.4 GPP Dyna Spine 31#
30.2" BOP
587 grains FOC 23% 10.9 GPP DSpine 42.8#
29.92" BOP
584 grains FOC 23.1% 10.9 GPP DSpine 44.2#
So all these shafts shoot extremely well and will group together. It's a coin toss between the 30.2 and 29.92 BOP set-up. I'm leaning toward the 30.2 BOP arrow for this elk season. I think it's gives the best of both worlds: heavy arrow and EFoc. Still have a ways to get to the 650 grain arrow but that's with another shaft.
So has anyone else experienced this? Any comments would be appreciated.
Thanks Much
Mike
I have found when I get much over 20% foc the point just kind of drags the bare shaft to about the same place as fletched. I can't bare shaft and figure much out with EFOC. I find it better to just shoot and change point weights for the best fletched and bare shaft flight and shoot combo's for the tightest groups.
I also find with 16-20% FOC and longer than needed arrows there is a spot I can bare shaft tune an arrow weak, stiff and jut right with points and slight length changes even though the arrow will not calculate on Stu's calculator and it should be weak by any account. I find that happens as I get around 2" more length than draw length. The only thing I can think of is that I get some kind of odd double flex in the shaft due to the overhanging heavy point.
I went to 600 spine arrows - full length with 400 grains up front from a 68 inch long 55lb @ 30 inch draw. they fly like bullets. The further forward you push the FOC the easier the arrows are to tune. Stu's calculator says they are way to light of spine. My bare shaft to fletched tuning says other wise. These arrows fly like bullets, even when I have a bad release.
I can get them to tune and fly great with everything from 175 to 300 grain points. My tightest bareshaft to fletched groups come with the 300 grain points loaded on the front.
What xtrema 312 said.