Okay… Kelski got up, stretched, and took a moment to clear her head. Grains per Inch was going to take some understanding. She wasn’t even sure it was something she could understand… even though she liked math. The Kelvic did a round of the training room, stretching, and kicking out her legs before she leaped up on the balance beam that was just a few inches above the ground and skipped down its length swinging her arms.
She tossed a leg up in the air, tried pirouetting, and then leaned down in a very simple cartwheel while balanced on the beam. It was what she needed to clear her head, some movement and grace. She tried two more, falling once off the beam as she tried to fit three cartwheels on it which was about one to many from her skill set. Landing on her rump, she laughed… unhurt, and got up to walk back to the bench.
GPI… grains per inch. How did she calculate that? Arrows, she knew, were propelled by energy produced by drawing the bow. It was like djed captured in the tense string. The energy transferred to the arrow when the crossbow string was released. The arrows weight would always determine how it flew… meaning its speed, drop rate, and its ability to penetrate the target. Her goal was to use the best arrow for the crossbow meaning maximum flight and penetration that the crossbow could handle without sacrificing speed or penetration.
Kelski was smart, but the thought of these calculations was enough to make even her head spin. According to Remmy, a badly weighted arrow … meaning the wrong one for the crossbow… could damage the crossbow and even hurt the crossbowman. So how did she figure it out? It wasn’t like she could just take the arrow upstairs to her workshop, rest it on a scale, and weigh it out. GPI was more complex. GPI stood for grains per inch. It was a formula that was calculated figuring in the arrows length, diameter, and shaft material. The nock, insert, point, and fletching wasn’t included.
Remmy stated light shafts were 5-6 grains per inch. Midweight shafts were 7-9 grains per inch, and heavy shafts were 10 gpi or more. And to top it off there were even more calculations. There was a GPP which was grains per pound and that included the weight of the shaft, insert, point, and fletching. Kelski’s mind was spinning at this point and she grabbed a fist full of hair, twisting it around her fingers, and frowning at the journal. GPP’s were 5-6.5 for light, 6.5-8 GPP for medium, and heavy weight arrows were over 8 GPP.
There were a series of calculations with examples which Kelski quietly went through… then went through again… then went through again. She then turned to her own bolts, was able to calculate the GPI of them, and nodded at the midweight range. She couldn’t calculate GPP on bolts because they had no fletching, nocks or heads. They were all straight steel shafts.