mjhamel

First of all, I just wanted to say thanks to all of you out there that have been chatting about tuning lately. I am sure learning a lot. I am fairly new to this site and have found it to be a valuable resource. Here goes,my bow is aReflex Super Slam with a 29" draw.I shoot Cabelas Carbon hunter arrows and are cutto 29.5". My draw weight is 62 pounds. My FOC is right at 11.5%. I use 100 grain NAP spitfire broadheads. I chronographed my bow the other day and was kindof surprised. The IBO speed of this bow is 300 fps and I was clocked at248 fps. Now I don't really care if I am only shooting 250 fps, but is this normal to be 50 fps below the IBO speed? I figured it would be about 20, maybe 30 fps slower. Also,according to the box that my arrows came in,my arrows should be theright spine. Would someone put my numbers in On Target or another program to see ifit is correct? Thanks for all of your help. Look forward to continuing the learning process.

Redneck Bowhunter

Im not sure here but I think that to get the IBO speeds the manufacturers use the lightest recomended arrow with no leeches or peeps in the string to slow it down, so that they can get it that fast, to make you think that is what you will be able to get.

mjhamel

And that's fine with me, I just wanted to make sure that nothing was wrong with my setup. Thanks.

Redneck Bowhunter

Well maybe someone else can back me up or correct me if im wrong, because im just not sure.

mjhamel

Based on my numbers I posted earlier, if I went to a 125 grain head, do you think my spine would still be correct? With the more weight you add to the front, would that make your arrow overspinned or underspinned? Just trying to get everything squared away before I go out and buy more broadheads of the same weight.

Arthur P

They come up with their "IBO rating" by using a bow set at 70 lbs with a 30" draw length, a 350 grain arrow and absolutely no string accessories. Anything that varies from that setup will give a different speed.

Less draw weight = less speed. Shorter draw length = less speed. Heavier arrow = less speed. Peep sight, string silencers, nocking point/loop = less speed.

Your bow is set up with 62 lbs (-8 lbs) and 29" draw (-1"). Your arrows are 8.7 grains per inch so they probably weigh in the neighborhood of 430 grains (+80 grains or so). Then subtract @ 2-5 fps for each accessory you have on your string. Actually, at 250 fps your bow is cooking along pretty darn good.

I assume you've got the 55-70 size arrows? You can try the 125's and see how they do. They could be pushing the envelope for those arrows, but you never know until you try.

mjhamel

Thanks for the reply Arthur, I am actually shooting the 65/80's, so I would assume that would actually help me out if I wanted to go to a heavier broadhead. Does that sound accurate?

davepjr71

I just ran a quick sim on OT2 and the number looks about right. I got 256 fps and I know that the program always seems high by 10 fps until you adjust the IBO for an arrow shot out of the bow.

Here's something though that seems off. The FOC I'm getting for the 65/80 is 10.43. With the 55/70 it's 11.42%.

I also found that your true IBO is more like 292 for your draw length.

The 65/80's are very overspined for your set-up. However, if the arrow is shooting well don't worry about it. Going to the 125 gr tips would help that out a little and your speed would only drop to about 243 fps.

Your other option would be to go to 55/70'd and shorten the arrow to about 27.5" and you'd be slightly overspined.

mjhamel

So basically, I should increase my draw weight and try 125 grain broadheads and that would get me closer to correctly spined arrows?

davepjr71

Yes, you'd decrease the dynamic spine by going to 125 gr tip and increasing the DW. Here's a print out of your set-up w/ a 125 gr tip and set at67 lbs. I've adjusted your IBO for the set-up that you posted before.