Archery Talk Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
128 Posts
Discussion Starter #1
Assuming all other factors are equal, what is faster; a 60# bow shooting a 300 gr arrow or an 80# bow shooting a 400 gr arrow?
 

·
Registered
Joined
·
60 Posts
Assuming all other factors are equal, what is faster; a 60# bow shooting a 300 gr arrow or an 80# bow shooting a 400 gr arrow?
speed will never take the place of accuracy. " man it was the biggest buck i have ever seen, i missed it so fast you could hardly see the arrow going over it's back". a really fast bow makes a miss really fast. figure out how many grains per pound your arrow is -- shoot 5 grain per lb. for 3-d and 6 grain + for hunting. pull as little weight as you can and be comfortable in the tree. don't grunt while drawing. !!!!
 

·
Registered
Joined
·
128 Posts
Discussion Starter #3
I just want to know the physics side, I have a 70# bow because thats what I'm comfortable with. And my FMJs with brass and 125s are a lot heavier than 5gpp, a lot quieter too. Call this curiosity. What has a greater affect on speed? Arrow weight or poundage? I picked the numbers based on 3D rules.
 

·
Registered
Joined
·
275 Posts
80# with 400 gr arrow will be faster, not much faster though. it will have alot more ke.
 

·
Registered
Joined
·
1,832 Posts
Assuming everything is the exact same except difference in draw weight. Both arrows should theoretically fly at the same speed since both are IBO 5gr's per pound of draw weight. The 400gr arrow however will arrive with much more momentum.
 

·
Registered
Joined
·
2,201 Posts
speed will never take the place of accuracy. " man it was the biggest buck i have ever seen, i missed it so fast you could hardly see the arrow going over it's back". a really fast bow makes a miss really fast. figure out how many grains per pound your arrow is -- shoot 5 grain per lb. for 3-d and 6 grain + for hunting. pull as little weight as you can and be comfortable in the tree. don't grunt while drawing. !!!!
??? not even close to answering the OP's question......:confused:


I would say that the speeds should be extremely close at 5gpp...... some bow designs may be more efficient % at 60lbs and some may be more efficient at 80lbs. I'd say most bows would be +/- 5fps with your 60-80 5gpp question.
 

·
Registered
Joined
·
2,737 Posts
The 80# bow will be much more efficient and should yield about 8 fps more than the 60#er.
 

·
Retired GI "still serv'n"
Joined
·
13,960 Posts
??? not even close to answering the OP's question......:confused:


I would say that the speeds should be extremely close at 5gpp...... some bow designs may be more efficient % at 60lbs and some may be more efficient at 80lbs. I'd say most bows would be +/- 5fps with your 60-80 5gpp question.
exactly......
I have tested every bow I have ever owned at min poundage and max poundage at 5GPP. To include the 82nd Airborne models at 40-70 lbs.
It depends on the efficiency of the cam/cams. In my finding most hybrid cams are a tad more efficient.
Bowhunter’s World magazine use to do efficiency ratings on certain bows in written evaluations back in the day….
calculators only go off of one efficiency rating, hence some bows will never shoot what the calculator states it should shoot and some bows will shoot a lil faster.
 

·
Real helos, have 2 rotors
Joined
·
10,241 Posts
Assuming everything is the exact same except difference in draw weight. Both arrows should theoretically fly at the same speed since both are IBO 5gr's per pound of draw weight. The 400gr arrow however will arrive with much more momentum.
Yep. That about sums it up.
 

·
Registered
Joined
·
2,846 Posts
I have tested 60 and 70 lb. bows, both shooting IBO weight arrows. The 60 lb. units seem to be a couple fps slower. Not enough to write home about, though.
 

·
Registered
Joined
·
5,222 Posts
5 Grains per pound is 5 grains per pound.....However, compound bow limbs are all made to the same width, within a few thousands of an inch , and the 80# limbs, being a little bit thicker for the same width, should store a slight bit more energy...Figure that a 70# bow shooting arrows @ 5 g.p.p. will usually shoot a couple F.P.S. faster than a 60# bow , all things being equal....So then, an 80# bow, in an Apples to Apples test, will likely be a couple f.p.s. faster than the 70# bow....Likely results would be somewhere between 5 and 8 f.p.s. between a 60# bow, and an 80# bow, at the same testing criteria.....Harperman
 

·
Registered
Joined
·
6,216 Posts
Most of the difference would be because of the fact that the string is now less weight per pound on the 80 lb bow. That's where the majority of the diff. will come from. If the strings were 33% heavier like the draw weight, the speed would likely be very close to the same.
 

·
Registered
Joined
·
233 Posts
This evidence is purely anecdotal, but I shoot a 403 grain arrow 320 fps at 80# and my friend shoots a 355 grain arrow 340 fps at 70# and when we both stand at the 30 or 40 yard bag and aim at the dot with our 20 yard pins the lighter bow and arrow hits considerably lower than the dot than the heavier setup does. They are two completely different bows but the KE of the two is very close. It seems to me that even if you get the same energy out of a bow at two different draw weights the heavier setup retains more down range. I don't know if this help but good luck.
 

·
Registered
Joined
·
533 Posts
speed

If you shoot a bow at 64lb that max out at 70lb at 5 grains a pound and shoot a 70 pound bow at 70lb at 5 grains about 6 to 8 feet different .
 

·
Registered
Joined
·
6,216 Posts
This evidence is purely anecdotal, but I shoot a 403 grain arrow 320 fps at 80# and my friend shoots a 355 grain arrow 340 fps at 70# and when we both stand at the 30 or 40 yard bag and aim at the dot with our 20 yard pins the lighter bow and arrow hits considerably lower than the dot than the heavier setup does. They are two completely different bows but the KE of the two is very close. It seems to me that even if you get the same energy out of a bow at two different draw weights the heavier setup retains more down range. I don't know if this help but good luck.
You could only compare that with the same bow/shooter. Differences in peep sight location (trajectory) and arrow FOC make that difference. Given the same bow and arrow FOC, the lighter/faster arrow hits higher at any reasonable range.
 

·
Registered
Joined
·
2,737 Posts
You could only compare that with the same bow/shooter. Differences in peep sight location (trajectory) and arrow FOC make that difference. Given the same bow and arrow FOC, the lighter/faster arrow hits higher at any reasonable range.
You are completely forgetting about momentum.The heavier arrow will shoot flatter than the lighter arrow.The miss distance,which is what their little side by side test is showing how a heavy fast arrow shoots flatter than a light fast arrow.


Ever wonder why so many 3-d pros shoot high poundage.I have shot with some that shoot 80# regardless of the organization because the arrows will be flatter.Even in ASA where 280 is the speed limit,they just build HEAVY arrows.
 

·
Registered
Joined
·
6,216 Posts
What you're trying to say I think is that the heavier arrow retains more energy down-range, so it keeps it's speed a little better, which is correct.

You can take 2 arrows of the same size, different weights, and drop them and they drop the same speed. The amount of time in the air is all that matters as gravity pulls down on them equally.

The arrow that gets there first doesn't drop as much. Does the slower heavier arrow hits a target faster at 70 yards than a lighter one? No. Even though it may keep a larger percentage of it's original speed and energy, it's still slower. Maybe they're going the same speed by 70 yards but the faster arrow was still going faster for the rest of the way.

It was my impression the poster was saying the faster lighter arrow hits lower. Either way, I'm just saying you can't compare arrow trajectory from 2 diff. bows and arrows with different FOC's and say it has anything to do with your arrow speed/weight.
 

·
Real helos, have 2 rotors
Joined
·
10,241 Posts
.....However, compound bow limbs are all made to the same width, within a few thousands of an inch , and the 80# limbs, being a little bit thicker for the same width, should store a slight bit more energy...
I think the opposite would hold true. In order to provide more poundage, the limb has more physical mass due to it's increased thickness. I doubt the calculation programs previously mentioned, account for that factor.

Since the limb has to move itself, in addition to the string, cams, cables and arrow, I believe it will result in arrow speeds very close to the lighter arrow/draw weight combination.

So close in fact, that other factors will determine the actual difference in arrow speeds. There WILL be a significant increase in kinetic energy and even more in momentum. However, in actual use, there will not be a significant difference in velocity. Either 5 ft away, or 30 yrds away.
 
1 - 20 of 22 Posts
Top