too light or bad FOC???

bigbuck270 · 04-01-2005, 07:33 AM

I just bought some new Gold Tip Xts 75 95. While I was there the bow shop owner was talking to us about the 75 gr rocket broad heads. So I descided to try them. However now I am shooting 75gr. So my question is, now am I too light or is my foc going to be off the gt site says my foc is 5.97% but that number doesnt mean much to me. I am shooting

Jennings trophy master 65#
28.5"
release
Gt xt 75-95

Any advice before I start tuning and shooting?
Thanks

adams · 04-01-2005, 10:12 AM

A low foc such as you have can have very negative effects on arrow flight. Read through this article for a better understanding of foc.

http://www.bowhunting.com/everythingarrows.asp?page=5

IMO a foc between 7% and 14% is best but you will find the larger number varring from as low as 10% to as high as 18%.

ijimmy · 04-01-2005, 10:41 AM

Usealy F O C does not concern me , but thats awefull low and being that you are shooting a pure carbon allready ,you need all the forgiveness you can get . between 9 and 14 would probably be better for you , maybe 100 grain heads would get you there . If they are fixed heads this would worry me .

If your shooting mecanicals , your foc will be less critical .

bigbuck270 · 04-01-2005, 10:54 AM

I just measured my arrows and they are 28.5 and the ballancing point is at 12.5" with the 75 gr. On the GT sited they said that the 100 gr is around 8.68%. Let me know your advice
Thanks

Karateman · 04-01-2005, 12:24 PM

The lowest FOC that Easton recommends is 7%. Based on that, I'd say that your too light with the 75 grain heads. Personally, I like to stay around 10%-12%.

adams · 04-01-2005, 12:44 PM

I played with the numbers and with a 100g head your foc would be 8.68%, with a 115g head it would be 10.18%, with a 125g head it would be 11.08%.
What I would suggest is find a shop that has a chrono and go there with a handful of diffrent field points. Shoot the 100g record the speed, 115g and recond the speed and then the 125g and record the speed. Then figure out which head gets you the most KE. The equation for ke is

Ke=(total arrow weight/450240)x(velocityxvelocity)

Once you figure which head gives you the most KE, it should be easier to choose a head weight and then eventually a broadhead to shoot. You'll likely fine the head that gives you the most Ke is also a head that give you an optimum FOC. Once tuned to the choosen weight you bow will be best matched for efficency.

If you can't find a shop around your way with a chrono maybe we could hook up and shoot some afternoon. I'm only an hour and a half away and I know of a shop about an hour from you that has a chrono.

nodog · 04-01-2005, 12:53 PM

Quote:

ORIGINAL: bigbuck270

I just measured my arrows and they are 28.5 and the ballancing point is at 12.5" with the 75 gr. On the GT sited they said that the 100 gr is around 8.68%. Let me know your advice
Thanks

Well, the site is set up well. It says to be between 8 and 12 so the ideal would be 10. If you want to use the 75's change the vanes on your arrows to feathers and it will be close. If the front of your arrow is to heavy you will have to set your nock to low to get the tail down. if it's to light the opposite will need to be done. Even then it most likely will not paper tune well at varying distances. You can also get some inserts to increase the weight of the heads and bring the foc up to 10.

I must say I think Gold Tips have done a very good job of helping their customers with the info they put out.

bigbuck270 · 04-02-2005, 12:41 PM

Adams

I would love to meet up with you some afternoon and pick your brain. I just dropped my bow off at Joe Jones to get a winners choice string put on. They said it will be done at the end of next week. Now I have picked a string and arrows, I just need to figure out a point weight and a broad head and then tune my bow to shoot them. Mainehunt just bought a new bow and the shop is setting it up but he is in the same boat as I am as far as fine tuning. Where is the shop you know of with a cronograph?

nubo · 04-02-2005, 01:27 PM

Most people use 100gr heads ,I'd stick with them just to keep your FOC up your still a bit low but not in a critical situation as for arrow flight ,you might still see some inconsistancy with your arrow flight but I'm sure it'll be a lot better than shooting with a 5%F.O.C. I would prefer for muyself to be at around 10 % which would be the mid mark.

nubo

adams · 04-05-2005, 01:24 PM

BB,

You, maine hunt and I should get together some afternoon. I called D&G archery in Wells and they have a chrono that we can shoot through (may cost a couple of bucks but I'll chip in as well to get you guys set up properly) They are open until 9:00pm so it should be easy for us to pick a time that works for everyone. If you want you can PM me and we can set a time and date.