[heilman181]

Ok, here is my dilemma. According to OT2 program, my LX at 80% let off with the 29" cam and 66 pounds with nothing on the string except for a Super Ball Peep ( I used 14 grains - ?) and string loop ( I used 12 grains - ?) shooting a 28" 391.2 grain Gold Tip Pro Hnter 7595 should be getting 285 fps.

I shot it thru my ProChrono Digital and come up with 274 fps. WHY? The bow is tuned, BH is set at 6 5/8" and cam rotation is perfect, ATA is falling somewhere around 35 1/4" and cam lean is correct. If I measure the actual draw length, I get 28" which would make my AMO draw length 29 3/4" (by adding the 1 3/4" to the actual.) If I plug my actual draw of 28" into On Target my fps would be 275 fps. If I plug in the AMO draw length of 29 3/4" I would be at 293 fps. WHAT SHOULD I DO? I am going to stop at the pro shop tomorrow and shot thru their chrono and see what I get, maybe my chrono is off! Have their been many inaccuracy issues with the archery programs. Maybe I am just having a hard time with 274 fps, I was hoping for something in the 282-285 fps range. Am I stretching it?

The reason I ask is I had a 28.5" cam on it before and the bow was out of tune and I was shooting the same arrow at 283 fps at 70 pounds. I switched to the 29" cam (which should give me more speed) so I backed the poundage off a little.

 

[bucktrout]

for every inch you gain about 10fps (so you could have picked up 5 fps) but for every 5 lbs you drop in weight you lose 10fps (so you should have lost 8 fps).

so if you were at 283 with your old set up should be around 280 (because you should lose 3 fps) so it looks like you only really lost about 6fps by switching the cam and backing down the poundage.

Basically your new rig is 98% of where it should be, using ballpark estimates so i would not sweat it. and perhaps it was unrealistic to expect a speed gain when you droped the lbs.

 

[heilman181]

for every inch you gain about 10fps (so you could have picked up 5 fps) but for every 5 lbs you drop in weight you lose 10fps (so you should have lost 8 fps).

so if you were at 283 with your old set up should be around 280 (because you should lose 3 fps) so it looks like you only really lost about 6fps by switching the cam and backing down the poundage.

Basically your new rig is 98% of where it should be, using ballpark estimates so i would not sweat it. and perhaps it was unrealistic to expect a speed gain when you droped the lbs.

I can see that, I guess I was focusing on what OnTarget 2 said too much!

 

[Cap't Kirk]

I have not been happy with OnTarget2 either. Found the calculations to be off from actual readings. 275fps is still a good speed for 66lbs. IMO

 

[heilman181]

I was wondering if my chrono was not reading correctly at first. I was going to stop at the pro shop and shoot thru theirs, but that may not be accurate either because of the indoor/outdoor issue. I would imagine that the only way to check two chrono's would be to place them in a straight line and shoot the same arrow over both of them.

 

[heilman181]

275fps is still a good speed for 66lbs. IMO

You are correct, 275 fps is definately fast enough at 66 pounds especially with almost a 400 grain arrow!

 

[bucktrout]

look at it this way.

IBO Specs - 30" draw/70lb draw weight and a 350gr arrow. IBO = 315

For every inch of draw length you go down you will lose 10 FPS = -10
For every 5# draw weight you go down you will lose 10 FPS = -8
For every 3 grains of weight your arrow is over IBO (5 grains per pound) you will lose 1 FPS = -20

So you should be around 276 fps with a bare string

For every 3 grains of weight you add to your string you will lose 1 FPS.

So your speed is very good!

 

[heilman181]

look at it this way.

IBO Specs - 30" draw/70lb draw weight and a 350gr arrow. IBO = 315

For every inch of draw length you go down you will lose 10 FPS = -10
For every 5# draw weight you go down you will lose 10 FPS = -8
For every 3 grains of weight your arrow is over IBO (5 grains per pound) you will lose 1 FPS = -20

So you should be around 276 fps with a bare string

For every 3 grains of weight you add to your string you will lose 1 FPS.

So your speed is very good!

I was not sure because 99% of bow companies go with the AMO draw length, which in my case is set at 29 3/4" out of a 29" cam bow!

 

[[email protected]]

OnTarget2! uses AMO draw length...not true draw or what the cam says DL is. You should use 29.75, because that's what you've measured as your AMO DL. If you're 3/4" longer than the cam's spec'd DL of 29", then you may have too long a string or too short a cable. Many manufacturers ship bows that have draw lengths longer than the advertised cam draw length. Having a fixed DL cam and strings and/or cables that don't create the DL spec'd for the cam might cause performance issues.

Things to check..

Is 66lbs the actual DW? Check on more than one scale if you can.

Can you set the bow at 70 and shoot a 350gr arrow thru a chronograph? Does this give an IBO speed that agrees with the published IBO velocity? You'll probably see some difference since your DL isn't exactly 30". Use "Your IBO velocity" instead o the manufacturer's stated IBO velocity in the field on the Equipment tab. You might try natural, outdoor lighting. I've noticed large swings in chrono readings when shooting my particular chrono indoors. I also see different readings when there is direct sunlight VS filtered (clouds) sunlight.

Have you calibrated the program to your specific setup? If not, you should try doing this. Shoot 2 arrows of different weights over a chronograph (DL & DW unchanged). Record the velocity difference for each arrow of different weight. Use the Efficiency from Arrow Weight calculation on the Calibration tab. Does this result in a different efficiency rating from the program default? Use this instead of the default value.

There are also calibrations for DW and DL efficiency. If you don't set these to you equipment, you're using the program default settings.

 

[preyquester]

i've owned a bunch of lx's & i shoot at 66# & 29" i shoot a 350gr arrow and every lx chrono's around 283-288 ( peep & loop)so account for arrow weight you are dead on.............

 

[heilman181]

Thanks for the input guys!

 

[heilman181]

I was wondering if my chrono was not reading correctly at first. I was going to stop at the pro shop and shoot thru theirs, but that may not be accurate either because of the indoor/outdoor issue. I would imagine that the only way to check two chrono's would be to place them in a straight line and shoot the same arrow over both of them.

OK, so I stopped in the pro shop and shot thru their chrono. I shot two arrows and the were 284 and 285 fps repectfully. I then checked my draw weight on their bow scale and it read 66 pounds! Not that I was "unhappy" before, something just did not add up correctly.

I guess now, I box up the ProChrono and send it back to Competition Electronics for a tune up!

 

[preyquester]

better do some ck'en your bow should not shoot that fast with a 390gr arrow about on for 350gr....:darkbeer:

 

[heilman181]

better do some ck'en your bow should not shoot that fast with a 390gr arrow about on for 350gr....:darkbeer:

I was wrong on the arrow weight, it is actually 386.75 grains, but that would not make that much of a difference. I will re-check all the specs when I get out to the garage!

 

[heilman181]

I was wrong on the arrow weight, it is actually 386.75 grains, but that would not make that much of a difference. I will re-check all the specs when I get out to the garage!

All my specs are right on! After I re-calibrated my bow scale and checked my draw weight, I was pulling like 67 pounds! I think light was my issue with my chrono too, I hung a florescent shop light in the garage last night to give the chrono more light and my arrows are shooting 282-284 fps respectively! Thanks guys!

 

[preyquester]

All my specs are right on! After I re-calibrated my bow scale and checked my draw weight, I was pulling like 67 pounds! I think light was my issue with my chrono too, I hung a florescent shop light in the garage last night to give the chrono more light and my arrows are shooting 282-284 fps respectively! Thanks guys!

cant beat that,you thought you had a slow bow & find out you got a extra fast one.now thats pure good luck.....:darkbeer: :darkbeer:

 

[heilman181]

cant beat that,you thought you had a slow bow & find out you got a extra fast one.now thats pure good luck.....:darkbeer: :darkbeer:

Good Luck - man-o-day that is a first! 99% of the time if I did not have bad luck then I would not have any luck at all!

 

[bucktrout]

that's smoking!!!! Don't know how fast my LX is right now, I'm set at 72 lbs with 29 inch. but i'm pushing a 482 grain arrow.

I do know it seems quite a bit slower than my bowtech, that has the 482 grn at somewhere around 285-290 fps

 

[heilman181]

I use the same setup for hunting and 3-D, so I wanted to be under the 288 fps limit. I should be around 70 lbs KE with that setup - poor deer!