Fps on mathew jewel?

hi all

i just ordered my new bow - a mathews jewel (26 inch draw and 55 pounds, ibo 325). Problem im having is all fps calculators work from a 30 inch draw length and 70 pounds draw length however with the mathew jewel, the ibo is worked out using a 29 inch draw and 60 pounds weight. If i have a 380 grain arrow and around an extra 20 grains on my string (peep and dloop) and working with my 26 inch draw length and 55 pounds draw weight, what would be my arrows fps and kinetic energy?

Also what would my bow be shooting at if it was tested at 70 pounds and a 30inch draw length. If i know this than i can use the fps/ke calculators.

thanks for your help

 

It's really hard to calculate what a bow will shoot at less than IBO specs, regardless of what type of bow it is. They all react differently to less draw weight, shorter draw length, etc. I would say you're going to lose at least 40-50 fps with that setup, so somwhere in the 275 fps range may be a good starting point. However, you won't really know until you get the bow set up and put through a chronograph.

 

From what my app says it would be around 238fps w/ 47ft-lbs KE. Which sounds about right with that setup. More then enough to hunt deer. At 70lbs and 30" draw - 320 fps with 86 ft -lbs KE. this is with 380g (arrow) 20g string weight.

this app is accurate too. If i run my setup

PSE evo 7 IBO - 335fps , 69.4lb draw weight , 29.5 draw length. 415g arrow setup + 20g string wieghts = 303fps 84ft lb KE

My local shops chrono says the same thing 302-304fps

 

Hi Dogfish

you need to remember this bows ibo is not measured using the normal conventional - 30 inch draw, 70 pounds like every other bow. The jewels ibo is 325 fps - that was what this bow shoots with a 29 inch draw and at 60 pounds of weight so the fps should be much faster than that.

To give an example, on a youtube review of the jewel they put a jewel set at 50 pounds and 25 inch draw weight through two chronographs with a 360 grain arrow and the normal dloop and peep. The speed this setup was getting was around 236 fps

 

If you have time it'd be nice to know more about the Jewel and how it compares to other bows you've shot. If wifey kills a buck this season I'll be suprising her with one.

 

jeffacarp i will be happy to tell you everything you want to know about the bow when i get it (I ordered it two days ago). I have called my local shop where i bought the bow and it turns out they have just bought themselves a brand new chronograph. Guess who will be breaking it in for them.

Let me know what you are wanting to know about the bow and i will make a post when i have had some time with the bow.

 

Its really hard to know. What I have read is about 10FPS per inch of draw length, about 2FPS per 5 grains of extra weight on the arrow, and around 3-5 FPS per pound of draw weight. But that all depends on what you have for a bow too. I would guess the Jewell would roll in a little less than these numbers since its really designed to be shot at lower poundages and weights. But the only real way to now is to run it through some chronos and find out. I say more than 1 because I have now ran mine through 3 and have gotten 270, 278, 289. I'm guessing the middle one is right but until I find one that duplicates one of these numbers I guess I just won't know. Not that it matters. I know its going to go through anything I'm going to shoot like a hot knife through butter anyway.

 

So then.. my calculation of 238 fps for your setup is about right. it would be closer to 240 probably.

 

backcountry.com has a calculator that uses the draw length, arrow weight, draw weight, string weight and IBO speeds to determine an estimated fps and kinetic energy.

A general rule of thumb is to subtract 10fps for each inch of draw length, 2fps for each pound of draw weight and 1fps for each grain of arrow weight, then for KE you would speed*speed*arrow weight / 450240.

At 26 inches and 55lbs you're looking around 250fps, then subtract from the extra weight on the arrow. The arrow weight used in IBO speed tests are 5 grains per pound of draw weight, so at 55lbs your IBO standard arrow would be 275 grains and anything over that would subtract additional fps.

 

I plot it around 233fps, with the arrow weight and string weight. The bow is rated at 325fps @ 29" and 60# according to their website, which is essentially the same as the Passion last year. I know I'd heard a few women have good reviews of the Passion, including a co-worker who placed in some national tournaments, but the did say the draw was a bit more aggressive than she was used to coming from shooting an Conquest. but she was surprised how nicely it felt in hand, and considering the shorter axle-to-axle, she was pleased with it's performance. You can cut arrow weight down quite a bit if you're really interested in FPS, but for optimal penetration in a hunting set-up, at 380gr/ you're probably right on.

 

Thankyou to everyone who replied. Im getting a general understanding on how this all works which is what i wanted. My local archery shop is going to help me setup and even papertune and then we are going to put it throught the chrono. Since i will be using my own arrows this should give me a good indication of my fps. Ill keep you all posted on the results. Btw i double checked my arrow weight last night and they weighed in at 374.8 grains so this might make a very very small change. Thanks again

 

Paper tune is only as good as the perfect release of the shooter, and will get you somewhere near close, but if you have space available, I'd recommend getting a pin zero'd at 10-15yds, then moving back to 20 with that same pin. Do a walkback tune, to center your rest, then a BH tune to fine tune that bow to where it needs to be to optimally use the energy in the best manner, as well as shooting in the most accurate manner it can when tuned to YOUR hands.