pros and cons of 125grain broadhead
07-21-2006, 08:33 PM
#2
Join Date: Aug 2005
Location: South Carolina
Posts: 171
RE: pros and cons of 125grain broadhead
I copied this off of the Mathews forum. Its long winded, but very informative.
Front/Forward
Of
Center
"The FOC value for an arrow indicates how far forward of the centre of the shaft the centre of gravity (COG) is located, expressed as a percentage.
If 'L' is the length of the shaft and 'D' is the distance from the centre of the shaft to the COG then the FOC = 100 x D/L.
e.g if the arrow is 80 cm long and the FOC = 12% then the COG is 12*80/100 = 9.6 cm in front of the shaft centre.
The FOC relates to two different aspects of shooting arrows, how the arrow behaves on the bow when being shot and how the shot arrow flies through the air.
In order to hit what you are aiming at the arrow needs to come off the bow straight and with no rotation. One of the principal factors which affects how the arrow comes off the bow is how it bends when being shot ("weak/stiff arrow"). For a given draw weight, shaft weight, shaft stiffness and length of arrow shaft the main way the amount of bending is affected is by varying the pile and nock weights. The heavier the pile weight or the lighter the nock weight then the more the arrow will bend. The shaft stiffness and associated weight depend on the shaft construction e.g. carbon arrow shafts are stiffer for the same weight then aluminium shafts. For the way the arrow behaves on the bow then the FOC is a guide to what the pile weight should be for the arrow to 'match' the bow in terms of coming off straight i.e. have the right amount of arrow bending.
Manufacturers publish recommended values for the FOC e.g an FOC of 7-9% for aluminium shafts, 11-16% for ACE carbon shafts. These values are largely based on the standard pile weights available for the shaft. In practice recurve archers often use higher FOCs by e.g. using specially made heavier tungsten points.
The reason the recommended FOC values are higher for ACE then for aluminium shafts is because the carbon shaft is much lighter then the aluminium for the same shaft stiffness. As the shaft is lighter the COG is further forward & the FOC is larger.
While the FOC value is limited by how the arrow behaves on the bow it also affects how the arrow flies through the air. This is related to the arrow total drag and the fletching action. As covered in the section on drag, the drag force on an arrow is split between two separate forces; one which acts through the arrow centre of gravity which acts to move the arrow and one which acts somewhere else, roughly around where the fletchings are which acts to rotate the arrow.
If you don't want to plod through the section on drag then A Rough Guide to FOC tries to give an idea of why FOC is so important to the drag properties of an arrow.
The principle drag effect on the arrow which makes you 'miss' with a bad shot or a gust of wind is the drag on the shaft. The drag area of the shaft with respect to moving the arrow about depends on the arrow FOC. If 'L' is the length of the arrow shaft and 'A' its diameter then the shaft area Fa which relates to drag movement of the arrow is approximately given by:-
Fa = LA(1-FOC/50)
This is only an approximation because any rotation (fishtailing) of the arrow will affect the value of the shaft drag area.
e.g if the arrow is 80 cm long and has a 0.5 cm diameter then:-
with an FOC of 8% the shaft drag area is around 80 x 0.5(1-8/50) = 33.6 square cm
with an FOC of 16% the shaft drag area is around 80 x 0.5(1-16/50) = 27.2 square cm
or to put it another way each 1% increase in FOC reduces the shaft drag area by about 2%.
The overall fletching area with respect to how the arrow flies comprises three elements:
- the effective area of the fletchings
- the shaft fletching area
- vortex shedding torque (expressed as an area)
The shaft fletching area is determined by the position of the COG i.e. the value of the FOC for the arrow. The shaft fletching area = 2 x D x A = 2 x FOC x L x A / 100. ( A, D and L as defined above). In other words the higher the FOC value the higher the shaft fletching area.
For example suppose you have a 80 cm long arrow with 0.5 cm diameter.
with a 7% FOC the shaft fletching area = 5.6 square cms
with a 11% FOC the shaft fletching area = 8.8 square cms
In practice the higher the arrow FOC the smaller the diameter is likely to be and also the size of the fletchings will probably be smaller (compare the typical fletching size/diameter of aluminium arrows to carbon arrows).
The FOC value also effects where the axis of rotation of the arrow is located as it fishtails etc. about. The arrow rotation point is always in front of the COG and as the COG moves forward increasing the FOC the axis of rotation moves forward. The overall speed of response of the arrow to fletching torque (its angular acceleration), i.e. how fast it straightens up, depends not only on the area of the fletchings but on the fletching torque and the 'rotatability' of the arrow, its moment of inertia. As the FOC increases the effective fletching area increases and the 'lever arm' increases. At the same time the 'rotatibility' of the shaft decreases (higher moment of inertia). Overall the arrow fletching response increases with FOC.
Having a high FOC for an arrow provides two principal benefits - better arrow groups and reduced wind sensitivity. When you aim at the gold but the arrow ends up in the black something must have changed the direction of the arrow. An arrow mechanically has to leave a bow going in the direction it was pointed and with its axis very closely aligned with the direction it's going. The arrow changes direction after it leaves the bow and the cause is arrow rotational energy (cartwheeling). The arrow flies in a curved path until this kinetic energy is removed by fletching drag (the stabilisation distance). Having a higher FOC results in faster energy dissipation (more fletching action) and because the drag area moving the arrow is smaller the amount the arrow direction is changed is reduced. The result is more forgiving arrow to bad tuning or a poor shot leading to reduced group sizes. In a wind the smaller drag area that moves the arrow results in reduced wind drift.
The downside to a higher FOC is because the offset angle between the arrow axis and the direction it's going will in general be smaller, the drag on the pile will increase; lift from shaft drag will be reduced and probably the arrow will be heavier and hence going at a lower speed. All these factors result in 'loss of sight mark'.
A recent example of how FOC affects flight comes from throwing the javelin. Javelins don't have any fletchings and because of the tapered end don't have any vortex shedding torque. Javelin rotation relies solely on shaft drag. The problem was that there was insufficient 'fletching' and javelins were often landing flat and skidding. Also because of the low FOC a lot of drag lift was being generated. Competitors were throwing javelins over 100m which was too for far safety at most stadiums. A couple of years ago the regulations were changed increasing the required FOC value. Now javelins rotate and stick in the ground nicely. The increased rotation rate has reduced the vertical drag component and the distances being thrown have been reduced to within safety acceptable distances."
Front/Forward
Of
Center
"The FOC value for an arrow indicates how far forward of the centre of the shaft the centre of gravity (COG) is located, expressed as a percentage.
If 'L' is the length of the shaft and 'D' is the distance from the centre of the shaft to the COG then the FOC = 100 x D/L.
e.g if the arrow is 80 cm long and the FOC = 12% then the COG is 12*80/100 = 9.6 cm in front of the shaft centre.
The FOC relates to two different aspects of shooting arrows, how the arrow behaves on the bow when being shot and how the shot arrow flies through the air.
In order to hit what you are aiming at the arrow needs to come off the bow straight and with no rotation. One of the principal factors which affects how the arrow comes off the bow is how it bends when being shot ("weak/stiff arrow"). For a given draw weight, shaft weight, shaft stiffness and length of arrow shaft the main way the amount of bending is affected is by varying the pile and nock weights. The heavier the pile weight or the lighter the nock weight then the more the arrow will bend. The shaft stiffness and associated weight depend on the shaft construction e.g. carbon arrow shafts are stiffer for the same weight then aluminium shafts. For the way the arrow behaves on the bow then the FOC is a guide to what the pile weight should be for the arrow to 'match' the bow in terms of coming off straight i.e. have the right amount of arrow bending.
Manufacturers publish recommended values for the FOC e.g an FOC of 7-9% for aluminium shafts, 11-16% for ACE carbon shafts. These values are largely based on the standard pile weights available for the shaft. In practice recurve archers often use higher FOCs by e.g. using specially made heavier tungsten points.
The reason the recommended FOC values are higher for ACE then for aluminium shafts is because the carbon shaft is much lighter then the aluminium for the same shaft stiffness. As the shaft is lighter the COG is further forward & the FOC is larger.
While the FOC value is limited by how the arrow behaves on the bow it also affects how the arrow flies through the air. This is related to the arrow total drag and the fletching action. As covered in the section on drag, the drag force on an arrow is split between two separate forces; one which acts through the arrow centre of gravity which acts to move the arrow and one which acts somewhere else, roughly around where the fletchings are which acts to rotate the arrow.
If you don't want to plod through the section on drag then A Rough Guide to FOC tries to give an idea of why FOC is so important to the drag properties of an arrow.
The principle drag effect on the arrow which makes you 'miss' with a bad shot or a gust of wind is the drag on the shaft. The drag area of the shaft with respect to moving the arrow about depends on the arrow FOC. If 'L' is the length of the arrow shaft and 'A' its diameter then the shaft area Fa which relates to drag movement of the arrow is approximately given by:-
Fa = LA(1-FOC/50)
This is only an approximation because any rotation (fishtailing) of the arrow will affect the value of the shaft drag area.
e.g if the arrow is 80 cm long and has a 0.5 cm diameter then:-
with an FOC of 8% the shaft drag area is around 80 x 0.5(1-8/50) = 33.6 square cm
with an FOC of 16% the shaft drag area is around 80 x 0.5(1-16/50) = 27.2 square cm
or to put it another way each 1% increase in FOC reduces the shaft drag area by about 2%.
The overall fletching area with respect to how the arrow flies comprises three elements:
- the effective area of the fletchings
- the shaft fletching area
- vortex shedding torque (expressed as an area)
The shaft fletching area is determined by the position of the COG i.e. the value of the FOC for the arrow. The shaft fletching area = 2 x D x A = 2 x FOC x L x A / 100. ( A, D and L as defined above). In other words the higher the FOC value the higher the shaft fletching area.
For example suppose you have a 80 cm long arrow with 0.5 cm diameter.
with a 7% FOC the shaft fletching area = 5.6 square cms
with a 11% FOC the shaft fletching area = 8.8 square cms
In practice the higher the arrow FOC the smaller the diameter is likely to be and also the size of the fletchings will probably be smaller (compare the typical fletching size/diameter of aluminium arrows to carbon arrows).
The FOC value also effects where the axis of rotation of the arrow is located as it fishtails etc. about. The arrow rotation point is always in front of the COG and as the COG moves forward increasing the FOC the axis of rotation moves forward. The overall speed of response of the arrow to fletching torque (its angular acceleration), i.e. how fast it straightens up, depends not only on the area of the fletchings but on the fletching torque and the 'rotatability' of the arrow, its moment of inertia. As the FOC increases the effective fletching area increases and the 'lever arm' increases. At the same time the 'rotatibility' of the shaft decreases (higher moment of inertia). Overall the arrow fletching response increases with FOC.
Having a high FOC for an arrow provides two principal benefits - better arrow groups and reduced wind sensitivity. When you aim at the gold but the arrow ends up in the black something must have changed the direction of the arrow. An arrow mechanically has to leave a bow going in the direction it was pointed and with its axis very closely aligned with the direction it's going. The arrow changes direction after it leaves the bow and the cause is arrow rotational energy (cartwheeling). The arrow flies in a curved path until this kinetic energy is removed by fletching drag (the stabilisation distance). Having a higher FOC results in faster energy dissipation (more fletching action) and because the drag area moving the arrow is smaller the amount the arrow direction is changed is reduced. The result is more forgiving arrow to bad tuning or a poor shot leading to reduced group sizes. In a wind the smaller drag area that moves the arrow results in reduced wind drift.
The downside to a higher FOC is because the offset angle between the arrow axis and the direction it's going will in general be smaller, the drag on the pile will increase; lift from shaft drag will be reduced and probably the arrow will be heavier and hence going at a lower speed. All these factors result in 'loss of sight mark'.
A recent example of how FOC affects flight comes from throwing the javelin. Javelins don't have any fletchings and because of the tapered end don't have any vortex shedding torque. Javelin rotation relies solely on shaft drag. The problem was that there was insufficient 'fletching' and javelins were often landing flat and skidding. Also because of the low FOC a lot of drag lift was being generated. Competitors were throwing javelins over 100m which was too for far safety at most stadiums. A couple of years ago the regulations were changed increasing the required FOC value. Now javelins rotate and stick in the ground nicely. The increased rotation rate has reduced the vertical drag component and the distances being thrown have been reduced to within safety acceptable distances."
07-21-2006, 08:50 PM
#4
Thread Starter
Join Date: Nov 2005
Location:
Posts: 175
RE: pros and cons of 125grain broadhead
thanks for the post dangolbowhunter.... can you summarize that?
07-22-2006, 09:19 AM
#7
Join Date: Jul 2006
Location: Salt Lake City, Utah
Posts: 56
RE: pros and cons of 125grain broadhead
It isn't a pro or con issue, really. The question is what weight of broadhead best fits your setup and your arrow.
The reason that most pro shops carry far more 100 gr. than 125 gr. and the reason that some manufacturers don't even make a 125 gr. broadhead is because the majority of archers are deer hunters shooting 5575 arrows and don't need or want the extra 25 grains.
Buy yourself some 100 gr. fieldtips and some 125 gr. fieldtips. Shoot them both at different yardages, see what happens. Unless you're a competition grade archer or you're shooting very light arrows, you won't see any difference at less than 30 yards. If you're into FOC formula, the extra 25 grains will translate into about 2% difference on a 29" carbon arrow. But again, it's all about how your arrows fly.
The reason that most pro shops carry far more 100 gr. than 125 gr. and the reason that some manufacturers don't even make a 125 gr. broadhead is because the majority of archers are deer hunters shooting 5575 arrows and don't need or want the extra 25 grains.
Buy yourself some 100 gr. fieldtips and some 125 gr. fieldtips. Shoot them both at different yardages, see what happens. Unless you're a competition grade archer or you're shooting very light arrows, you won't see any difference at less than 30 yards. If you're into FOC formula, the extra 25 grains will translate into about 2% difference on a 29" carbon arrow. But again, it's all about how your arrows fly.
07-23-2006, 02:55 AM
#8
Nontypical Buck
Join Date: Feb 2003
Location: Harford Co Maryland USA
Posts: 4,966
RE: pros and cons of 125grain broadhead
I've always shot a 125 grain BH, but now I shoot it for a reason. My drawlength is 27" and, consequently, I have to shoot a 4560 arrow even though I'm shooting 70lbs. Because of this, I want a 125 grain BH both for the added weight AND [more importantly] the higher FOC I get from them. I shoot 125 fieldtips as well and both deliver excellent groups and all the ranges I shoot.
07-23-2006, 08:36 AM
#10
Nontypical Buck
Join Date: Jul 2006
Location: Monroe County, IL
Posts: 1,188
RE: pros and cons of 125grain broadhead
The 125's are of course heavier but also give a larger cutting diameter.. I personally use 100's and have always used 100's.. Just depends on what your set up for.. I would choose what grain tip you want when your setting up your bow and your arrows.. Use charts such as on Eastons website to determine the correct weight tip, arrow, draw length, lbs of pull etc...
The 125 are better for some setups and the 100 will be better for some.. Just depends.
As far as hunting goes they will both work just fine..
The 125 are better for some setups and the 100 will be better for some.. Just depends.
As far as hunting goes they will both work just fine..