Adjusting for draw weight vs arrow weight

[sf jakey]

I currently shoot a 75lb bow and a 482 gr arrow going about 277 for elk. I want to reduce my draw weight to 65 for extended practice and blacktail deer, but I’d like to maintain my current trajectory. How much should I be looking to reduce my arrow weight by to match the drop in draw weight? I know it’s not exact, but a general idea. Thx

 

[Bump79]

I made up this calculator just for this purpose. Personally, I'd probably try to keep my arrow shaft as close in outside diameter as possible. I would reduce down in point weight You likely will need to adjust down in spine.

Arrow Speed, KE and Momentum Calculator — The Arrow Builder

Many online arrow/bow speed calculators use an oversimplified calculation to determine arrow launch velocity. This results in inaccurate results, especially at higher grain weights. Increasing arrow mass always will lead to marginal increases in KE, meaning the bow gets more efficient as grain wei

www.thearrowbuilder.com

I'm not sure on your specs exactly but around 420 grains would keep you right around 277 fps.


You can use this side by side arrow build comparision to play around with different shaft options and front weight to get to 420 grains.

Arrow Builder | Build Your Perfect Arrow Today — The Arrow Builder

This tool is designed to allow archers to play around with different builds and see what the difference might be. This will help create high-performance arrows tailored to your needs. Explore our tools and get a personalized quote now.

www.thearrowbuilder.com

 

[Mighty Mouse]

I would guess you’ll need to reduce arrow weight by 75-80 gr to maintain your current speed after dropping DW from 75# to 65#.

 

[Shooter Mike]

Generally, 2 feet per second per pound of draw weight and 3.5 feet per second per 10gr of arrow weight, IIRC.

 

[michaelt3719]

just browsing, little late to the party but this site here will tell you what you're looking for.

ArcheryCalc – Backcountry Bowhunting

backcountrybowhunting.com

 

[Bump79]

just browsing, little late to the party but this site here will tell you what you're looking for.

ArcheryCalc – Backcountry Bowhunting

backcountrybowhunting.com

This calculator isn't right and has lead to a lot of incorrect calculations. Most of these online calculators are based off of a generic rule of thumb that only works for a very narrow range of setups. The further you are off from IBO, the less accurate it becomes. Also, KE never drops off like the images I show below. You can think about your bow as a fixed KE that marginally increases KE with arrow weight. KE and arrow mass are the driver for speed - so this is another fundamental bust in these calculators.

I'd use the link I shared or the Ashby calculator. These are the only two relatively accurate speed calculators I've ever found.

 

[michaelt3719]

This calculator isn't right and has lead to a lot of incorrect calculations. Most of these online calculators are based off of a generic rule of thumb that only works for a very narrow range of setups. The further you are off from IBO, the less accurate it becomes. Also, KE never drops off like the images I show below. You can think about your bow as a fixed KE that marginally increases KE with arrow weight. KE and arrow mass are the driver for speed - so this is another fundamental bust in these calculators.

I'd use the link I shared or the Ashby calculator. These are the only two relatively accurate speed calculators I've ever found.

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Allll righty-then. Found that a couple yrs ago, can't vouch for its accuracy just knew it was there and directly related to the discussion.
I've read the ibo ratings are usually inflated from being under "ideal test conditions" - whatever that term covers. Didn't know about the KE never dropping thing. That's getting way above my pay grade as far as technicalities. I was just interested in about how much speed I lost from adding 75 grains a few yrs ago after missing fwd just enough and not getting through a shoulder, and then reading how much weight helps penetration. I bumped into that calculator which seemed to tell me.
Apparently not overly accurately. But no matter what I sure like 475 better than 400ish.

 

[Bump79]

Allll righty-then. Found that a couple yrs ago, can't vouch for its accuracy just knew it was there and directly related to the discussion.
I've read the ibo ratings are usually inflated from being under "ideal test conditions" - whatever that term covers. Didn't know about the KE never dropping thing. That's getting way above my pay grade as far as technicalities. I was just interested in about how much speed I lost from adding 75 grains a few yrs ago after missing fwd just enough and not getting through a shoulder, and then reading how much weight helps penetration. I bumped into that calculator which seemed to tell me.
Apparently not overly accurately. But no matter what I sure like 475 better than 400ish.

Yeah, I didn't mean to seem like I was jumping on ya. It's just something that drives me nuts - most of these places put out the calculator just for the clicks when they are googled. Doesn't matter if they are right or not. They can be substantially off at times.