Ask The Experts – GPI

Q: GPP, GPI, what’s that all about?

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A:Quite often we are asked: ‘Can I use carbon arrows?’ Often the answer was: ‘No! Use wooden arrows only.’ Being a bit of a rebel however, that did not sit right with me. Why not? What are the arguments? Are we just repeating other people’s opinions? After all, bows don’t have eyes…

The bow is a spring; energy stored by drawing the bow to your draw length is then transferred to the arrow. If the arrow is too light, energy is left in the bow, getting dangerously close to dry loosing the bow. Signs of this happening are massive hand-shock, lots of noise, and string slapping on to the (recurved) limbs.

Getting back to the original question, ‘What is GPP or GPI?’ those stand for ‘grain per pound’ and ‘grain per inch’. This is relevant to the bow’s energy transfer because every inch of an arrow shaft weighs x amount of grains, and fletchings and the point add some more. This makes up the overall arrow weight. Most modern arrows have GPI specifications stated by the manufacturer. However, with traditional arrows, this is not so frequent. Most bows have certain thresholds (do check with your bowyer) of minimum weight load (grain per pound). In our case, most often this is 10 grains per pound. So a 45lb bow would require a load of 450 grains in arrow weight.

Make sure these figures match and your bow will last longer with a higher efficiency and better performance.

Magén Klomp


The Glade Ask The Experts – in association with Fairbow


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