davepjr71

bruce

Have you thought about shortening the arrow a little to up FOC? It will probably only give you a small percentage change but will raise the FOC. Making the arrow 30" will give you about 3/4 of a percent increase if I have your arrow numbers close in Ontarget.

Also, anything that is done to lighten up the nock end will increase FOC.

passthru79

Wow 16 and 17% FOC, I think mine is almost 11%. 27inch goldtip prohunter with three blazers and a wrap on the back, and a 100 grain tip. Whatever works, think my total arrow weight is about 360grains.

brucelanthier

I use OT2 also and if I understand it correctly I thought the shaft length is just the shaft not counting the nock or the insert/point. That is why I made the shaft itself 30". Adding the point and the nock made it longer. Actually I am about as high at FOC as I am wanting to go with this particular arrow.I may experiment with some heavy inserts so that I can use a different point/broadhead ( I have6 more to experiment with).

brucelanthier

Something interesting I noticed after making this arrow and putting the measured FPS numbers into OT was that my bow speed increased. I adjust the IBO speed so that the calculated speed matches the measured speed and I had the IBO speed at 285 for a lighter (434gr) arrow. When I adjusted the IBO speed to get the calculated speed to match the 534gr arrow I had to increase it to 293. I am assuming that there was a more efficient energy transfer to the arrow with the heavier weight. I thought that was interesting.

brucelanthier

The next arrow I want to try and make will be 500+ grains but about a 12+% FOC. That won't be for a while though.

davepjr71

Something seems off on the increased IBO speed. You shouldn't need to adjust the IBO speed of your bow. It is what it is. Just change the input numbers for the heavier arrow.

I've had the same thing happen to me with OT2. I was checking about 4 different arrows. The speeds were all over the place and then realized thatI needed to reset my basic inputs and then it would work fine.

The 500 gr arrow with a 12% FOC isn't to hard to build. Just get an arrow with camoon it that weighs about 12.2 gpi. Blazers, and about 29.5 inches long.

passthru79

I use to shoot a 75grain tip, that made my FOC pretty crappy. But still had very good arrow flight and awsome penetration.

brucelanthier

This is from the help file of OT2:
The bold is from OT2, the italics and underline are my highlight. If I read this correctly then When I take my known arrow weight (and known weights of all the parts - 22gr insert, blazers weighed @ 6gr each, nock weighed @ 12gr, 200gr point and the shaft) and shoot it and then get my known chrono speed then I should be able to adjust the IBO speed to match my known chrono speed.

OT2 is only as accurate as the numbers put it. I put in as many measured, known numbers as possible. Anyway all I did was synch the program calculation to my known velocity as outlined in the help file. And it seems that the numbers say my bow is more efficient at a higher arrow weight.

brucelanthier

I am new to bow hunting but it seems to me that with todays equipment we can probably get away with a lot of stuff way outside the recommended average margins and still be very effective.