I am currently shooting a 400 spine Easton Carbon Aftermath arrows that has a GPI of 8.8 and Easton Bloodline arrows 400 spine with a GPI of 7.7. Which is the faster arrow. My bow is a PSE stinger 3g. Draw weight 55lbs and draw length 27.5. I shot my first 3d shoot of the year and I was talking with my buddies about shooting faster arrows or cranking up the weight a little more. Shooting the draw weight that I am currently shooting what's the lightest spine and GPI that I can shoot to gain a faster arrow??
The lightest spine at the same weight? I wouldn't go under 400. You may be able to get away with a 500 spine. If you did decide to go a 500 spine, i sure wouldn't go up on your weight. 275 grains finished arrow weight is 5 grains per inch which is the lowest recommended. Your bow is probably shooting between 250-260fps with the 7.7 which is probably in the 340 grain finished range. Give or take some grains. I don't know what inserts, vanes, nock or weight tip you are running so that's my ball park estimate. If you get it down to 300 grains you could get up to around 270fps. Your shorter draw length and the IBO on that bow is going to limit you a good amount on speed. Your arrows are plenty light enough for 3D. I recommend you work hard on yardage judging and spend the money on an adjustable sight. That is if you don't have one. Break out the range finder and take it with you everywhere you can. When you get out of your car at Walmart, judge the cart left in the parking lot then shoot it with the range finder and see where you are. Walk the woods and judge different elevation changes, across creeks and going from different lighting changes. If you are good with yardage, speed only helps when you make a mistake in yardage. I think to many (including myself in the past) have relied on their equipment to make up for their short comings on yardage judging.
I failed to mention arrow tip weight has some to do with your spine as well. The heavier your tip weight basically weakens the spine. You could run say a 500 spine with 85 grains up front and help the arrow tune and lighten the weight. It does change your FOC. If you are building an arrow for target, the general consensus is a lower FOC is required. I try to stay between 10-12% on target and around 14% on hunting arrows. Higher FOC (Front Of Center) helps or seems to in my experience with penetration and arrow flight. That's not so much a concern with a properly tuned arrow/bow combination for target.
You can easily shoot a 500 spine at your specs assuming the length is shorter than your draw length. You can shoot under the 5 gr per lb as long as you don't exceed 280 fps for ibo (assuming the rule hasn't changed) But getting lighter than 275 gr will be hard to do so I doubt that will be an issue. Sent from my SAMSUNG-SGH-I317 using Tapatalk
Im assuming you want to stay in the hunter class. An easton lightspeed 3d 500 spine with screw in inserts shooting a 75 gr or 65 gr point if you can find then will suit you well. Easton diamond vanes at 2.35 length would be a good match. Sent from my SAMSUNG-SGH-I317 using Tapatalk
