this not going to be easy due to the fact as soon as the poundage increases the spine also has to increase he might try the same weight but with a lighter arrow due to the fact he will lose about 20 to 30 fps my son had the same idea he now shoots the same brand of arrow cut 3 inces shorter than mine and the spine also went down…:)

Looper wrote: Can anyone help me figure out a problem? Let’s say that my brother wants to shoot the same weight arrow as I do at the same speed as mine out of the same type bow, but he has a 2.5 inch shorter draw. What pound bow will he need? My bow is 48# @ 30.5″ (Hill longbow).

I assume your brother doesn’t have a bow yet, since you asked what poundage he would need. He would probably want something a little heavier, because his draw weight on your bow would probably be a touch under 45# at his length. I would say, and this is just guessing, that he would want something between 50 and 55# at his length. From there, you can most likely tune the bow to the arrows by playing with brace height and nock point.

The other option, and better in my opinion, is for him to buy the bow that is best suited to him, and set up his own arrows for his bow.

Even if you have two bows that are supposed to be identical, they will most likely tune differently and require slight differences in the arrows used. It’s much like two drag racing cars that are built exactly identical. One will most likely perform differently than the other. Just how it goes. No matter how close of tolerances we use, there is always something different. Different piece of wood, different density of arrows from one to the other, etc, etc.

Good luck.

Michael.

Looper wrote: This is more of a theoretical exercise. We were trying to figure out the advantage of a longer draw. Since I pull 30.5″ with my Hill, and he only pulls 28″, what pound would he need to pull to shoot the same weight arrow at the same speed as me.

Or, a bow pulling 50@30.5″ equals ?@28″.

Or, if he shot my arrow out of his bow, how many fps would he lose over mine?

Or, if I only pull my bow to 28″, what would be the fps loss?

Well figuring out the poundage is easy, just throw the bow up on a scale and measure it at 28 and 30.5″. You’ve got to figure out the poundage increase past 28. If you are at 50@30.5″ I bet you are somewhere around 42# at 28″ out of that bow.

30.5 isn’t that much longer than a 28″ in regards to arrows IMO. The arrow will weigh more overall depending on how much GPI it has. To compensate he could go down in weight on the tip and still be fine….right guys? 😕

No…I don’t think I’m missing it.

By my logic, it should be a 58# bow. He is probably 8# lighter with your bow at his draw. Tack that on to 50# = 58#

IF that is how much your bow stacks.

58# is going to throw 500 grains faster than 50#, no matter what the draw length is. It’s like powder in a rifle cartridge. My 7mm Mag with 63.4 grains of R22 is going to throw my 175 grain bullet faster than 55 grains of R22 out of the same gun.

Michael.

According to stu’s calculator, it is the same speed if you’re using the same weight arrow and the weight is the same at the respective draw length. Makes some sense to me even if its not right. I mean just because its on the string longer it is still pushing the same mass with the same force so why should it be faster?

Best way to find out tho is with a chrono and two bows at these specs.

Looper wrote:
I read somewhere that Dan Quillian said an inch of draw length is equivalent to 10 pounds of draw weight. I’m not that optimistic. So what is it?

I don’t know what Dan Quillian did or didn’t say. However, Fred Bear, in The Archer’s Bible, Chapter 1, page 10, states, “Not all archers of course use a 28-inch arrow, and it is obvious that a person with a 26-inch draw will be drawing less weight, while one with a 30 inch draw will be increasing the draw weight. In most makes of bows, this loss or gain in draw weight will be about 2 to 2 1/2 pounds for every inch the draw is shortened or lengthened.”

Now, take it or leave it, but that’s a direct quote. As for my comparison between powder charges for my 7mm, that was merely a comparison of two similar, but different forces propelling the same weight of object. Best comparison I could come up with off the top of my head. I don’t believe that the speed between 50@30.5 and 50@28 is going to vary all that much. It’s still the same force applied to a given (500 grains) weight.

Michael.

If you take a 50@28 and use the same weight arrow but draw it 30.5 you’re looking at a speed gain of 10fps.