FPS ratings

crissmand · 10-10-2003, 08:49 AM

Can anyone tell me the difference between IBO and AMO FPS ratings you typically see advertised with bows?

Rangeball · 10-10-2003, 09:03 AM

Stated IBO fps= 70# bow with a 30" draw shooting a 350 grain arrow (5 grains per pound).

Stated AMO fps= 60# bow with a 29" draw shooting a 360 grain arrow (6 grains per pound).

Danny45 · 10-10-2003, 09:06 AM

AMO is the manufacturers trying to establish a standard for rating bow speeds. It' s the speed of a 540 grain arrow out of a 60 lb bow.

IBO was started (unsure by whom, maybe the IBO) where the speed is what a 70 lb bow will shoot a (I think) 350 grain arrow. That' s keeping in the safety standards of 5 grains of arrow for every lb of draw weight.

Anybody out there with better info, please post for crissmand.

crissmand · 10-10-2003, 09:17 AM

Thanks...so given that my bow is set for 63 lb. draw weight and assuming the carbon arrows I just bought are typical weight along with my 115 muzzy broadheads...I can probably assume my system delivers FPS performance somewhere near the middle of the IBO and AMO ratings???

Rangeball · 10-10-2003, 09:33 AM

That' s a fair assumption

And I was wrong on the AMO, I think it is using a 540 grain arrow at 60#s with a 29" draw, not the 6 grains per pound I posted above... I think I' ve killed too many brain cells...

If you post what the AMO and IBO ratings are for your bow, what the bow is, what cam option, how you have it set up, what' s on the string, the make, model and length of your arrow, total arrow weight, guys here are very good at getting you a pretty close estimation of what you may be doing...

Arthur P · 10-10-2003, 09:39 AM

After IBO came up with their 5 grains of arrow weight per pound of draw length and 80 pounds max draw weight rule, people started seeing how much speed they could get out of their bows and still be ' legal.' The manufacturers picked up on it, decided most people would be shooting 70 pounds instead of 80, pulled the 30" draw length off the AMO rating and bingo! the ' IBO rating' was born. IBO never had anything to do with setting up any kind of rating.

All IBO did was write a rule for their tournaments to keep idjits from hurting themselves and others by too light of an arrow off too much bow. Lots of people were hurt in the early days by exploding bows, boneheads shooting 300 grain arrows at 90 pounds draw - nothing more than a barely restrained dry fire. It was entirely a safety issue for IBO. Nothing more, nothing less.

The ' IBO rating' has never been officially adopted by the industry, but they sure sell a lot of bows by advertising it. They even adopted a light arrow version of the AMO spec in 1999, a 360 grain arrow at 60 pounds and 30" draw but they have never once used it in their advertising. Very few people know the light arrow AMO rating even exists.

6 grains per pound was the industry standard for a safe arrow weight until shooters demanded bows that would handle 5 grains per pound and not rattle when they shook them after a few tournaments.

Anyway...

crissmand, whether you get between AMO and IBO rated speed with your bow depends on how long your draw length is. IF your draw length is 30" or over, then you can safely bet you' re in there somewhere. If you' re drawing 28-29" you might be. If you draw less than 28" , you might very well NOT be.

Rangeball, grab another cup of coffee!

Standard AMO rating - 540 gn arrow, 60 pounds, 30" draw. Light arrow rating - 360 gn arrow, 60 pounds, 30" draw. The AMO ratings are spelled out in specification ASTM 1544-99.

Rangeball · 10-10-2003, 09:48 AM

Crissmand, ignore me, I have no fricking clue what the AMO rating is, obviously...

Art, I swore I read somewhere it was 29" draw. I think it was in a Norb Mulaney review, but I must have been mistaken...

Arthur P · 10-10-2003, 09:57 AM

Rangeball, I can' t help it. My pea brain is so cluttered up with obscure information that I can' t hardly keep track of it all. But I guarantee ya, I' m hell on wheels when it comes to playing Trivial Pursuit.

crissmand · 10-10-2003, 10:52 AM

Great info...thanks! My bow is a Reflex Growler. It' s a 50-60 lb variable draw weight, but as a result of limb length being an inexact science, it registers 63 lbs when it' s maxed out...which works for me. I' m shooting 115 grain muzzy 4-blade broadheads and my draw lenght is 28 inches. I have mid-grade Easton Carbon arrows...so my hasty estimate would be that I' m getting about 240 FPS....sound close??

Black Frog · 10-10-2003, 11:13 AM

Range-

Norb occasionally throws in a 29" AMO draw at 60#' s for comparison with his standard 30" AMO measurements at 50# and 60#, like he did in his review of the Darton Rampage.

The IBO rating never specified a 30" draw, simply 5gr/pound for equipment safety. Nowhere does the manufacturer have to adhere to 30" draw at 70#' s (unless they specifically state it). A manufacturer could rig up a bow at 74#' s and 31" draw with a 370gr arrow, put it through a chrono and call that its " IBO Rating" .... [X(] You can see how some manufacturers could fudge speed ratings. The AMO paramters are very specific and much more telling. But the AMO numbers don' t look nearly as flashy on advertisements as the big-number IBO speeds do.