Speed Question

[Texastaxi]

My Synergy is set up at 27", 65# and shoots a 400 gr arrow at 275 fps.
What's the approximate speed when I bump my arrow up to 630 gr?

[Mike Javi Cooper]

My Synergy is set up at 27", 65# and shoots a 400 gr arrow at 275 fps.
What's the approximate speed when I bump my arrow up to 630 gr?

A rough number is 1 fps per 3 grains of arrow weight...

[Texastaxi]

So, you're saying I'll loose about 76 fps?

LOL, my Synergy now shoots 200 fps!
Not such a speed demon now are ya, Kevin Strothers?

[TX kyleboy]

Never heard anyone quote that rule of thumb (3 fps per grain) but it is right on by my experience. When I change my set up to shoot 3D all I change is the Sure-Loc sight and the arrow. I drop about 140 grains and pickup up about 40 fps.

[Mike Javi Cooper]

So, you're saying I'll loose about 76 fps?

LOL, my Synergy now shoots 200 fps!
Not such a speed demon now are ya, Kevin Strothers?

A lot of that will depend on where the 400 grain arrow fell in the efficency range of the bow... if it was below the peak.. you may lose less and if it were above you might lose more... I suspect you will lose a little less..

My Prestige loses 32 fps going from 477 grain to a 630 grain arrow which is 153 grain difference

[rocky]

The math says 200 fps (app) so you'd actually lose 12 lbs of ke, and we know that's not right.You will have to shoot 220 to get the same ke, but if you shoot 230, you'll gain about 7 lbs ke which should be about right.
Hope for 230 fps.
In the math, there is a diminishing amount of loss as arrow weight increases, and a large ke gain is only realized with a substantial increase in arrow weight.

[Mike Javi Cooper]

The math says 200 fps (app) so you'd actually lose 12 lbs of ke, and we know that's not right.You will have to shoot 220 to get the same ke, but if you shoot 230, you'll gain about 7 lbs ke which should be about right.
Hope for 230 fps.
In the math, there is a diminishing amount of loss as arrow weight increases, and a large ke gain is only realized with a substantial increase in arrow weight.

Exactly why Ke is a poor way to judge penetration potential….. momentum is a better measuring scale…

[rocky]

Exactly why Ke is a poor way to judge penetration potential….. momentum is a better measuring scale…

I've questioned this often, but don't know a formula for momentum.

[Mike Javi Cooper]

I've questioned this often, but don't know a formula for momentum.

Rocky here is a good article on the equation... http://www.alaskafrontierarchery.com/Articles.html

Or just use this equation... which will get you close without a whole lot of head banging...

Arrow weight X 2.2 X Arrow speed - divided by - 1543.2 divided by 10 divided by 32

[Bill]

I found that shooting an arrow 100 grains less than my CT Rhinos (500 grains vs. 400 grains) increased my speed by 20 fps. Using that math, going to 630 would result in around a 45 fps decrease for you- all things being equal, which they are not.

I don't believe that KE is the important thing- arrows kill by cutting, not impacting and destoying organs by transferring energy. But this is a Ford vs. Chevy argument with no clear winner.

A heavier arrow will be easier to tune (slower), a quieter bow (more mass to absorb energy and thus sound), but at the cost of increasing your pin gap and impact point with uncertainty in estimating the distance to your target.

My answer plus 2 cents.

[Texastaxi]

Rocky, I was hoping you'd find this thread.

All of you, got to my next question without me even asking it. I know from trial that the heavy arrows seem to get better penetration, or at least they did on my buffalo. I was just curious as to what the ke gain would be, if any. We all know that our predecesors (and Legdog) killed critters with bows that wouldn't shoot 200 fps and sounded like a 22 rifle. If nothing else, the increased weight makes the bow "feel" better when you shoot it and it does noticeably quiet it down.

I think I'll make a trip to a shop this week and get some real numbers to see how close ya'll were. If it's still shooting around 230, I'll be VERY impressed.