I'm doing a lot of research on arrows and such. Why / how would you know you need a 125 gr BH vs. a 100 gr. BH? Is this all based on tuning? Is it based on your arrow? Weight? What's the deal!
It depends on a lot of factors but the bottom line is that it effects your tune. You can change the way your arrows spine reacts by increasing or decreasing your tip weight. The thing is that you can also accomplish this by increasing/decreasing draw weight and arrow length. So if you're set on a certain tip weight (for increased arrow weight and FOC for example) you can use the other variables in tuning your arrow to your bow or vice-versa. Basically, if one or two of the three variables (draw weight, arrow length or tip weight) are fixed, you can vary the other(s) as necessary to come to a tuned bow and arrow set-up; assuming that you selected an arrow spine that is within range to begin with.
Great post Rob!!! Indy, I can tell you for me, I set my arrow up around having a 125gr tip, as the better FOC will help arrow flight and penetration. FOC makes a big difference, that extra 25gr don't make a huge difference, but if you set a bow up for a 75 or 85 gr head vs. a 125gr head there is a SIGNIFICANT difference in arrow flight. That higher FOC "leads" the arrow to the target....
I'm in the process of building some 29.5" shafts with a 315 grain head and 100 grain insert. I can't wait to see what the FOC is going to be on these tanks! :D
TRAD BOW??? You're surely not gonna shoot those out of a compound..... I always liken it to throwing plastic vs. real darts.... Makes a lot of guys understand FOC in a hurry...:D
Just got the 80 lb. limbs for my Z28 yesterday... by all calculations I'll be able to throw them just faster than a water buffalo can run.
So what exactly does FOC stand for? I have my theory, but a theory is like an opinion is like an a-hole... If you had a light arrow, and a 125 grain tip, would there be too much "flex" if you will. Let's say your total arrow weight was in the 360 range, but your tips were 125. I'm just throwing out ideas trying to get a feel for what people have tried.
Rob, What spine are the arrows??? And do you have weight tubes inside to stiffen the spine or anything..... That sounds like a scary combination for a dangerously weakened spine.... Not that I'm doubting you, because I know you definitely know your stuff, just wondering..... The idea when building the arrow is to design it for the optimal flight and penetration for hunting for me.... While also taking into consideration speed as a lesser concern. The 125 will weaken the spine of an arrow ever-so-slightly, that is where you can change length of the arrow, and maybe even spine to get optimal spine. Most "spine charts" are considerably OFF because they were designed when the avg. bow shot about 300fps IBO rated, with most bows now exceed that rating, they also have MORE stored energy which is what you design the spine around. If you add a little front weight, then you weaken the spine so you have to fine-tune the arrow to correct length, to balance it out. Front of center allows the front of the arrow to guide it. Why I used the plastic vs. REAL darts comparison. Because those "plastic" darts weigh so much less and tend to not have a heavy front they don't fly worth a damn, but the real brass darts fly like...well... DARTS!!! Even if you put the same POINTING tip on a plastic dart it would never penetrate as deep as a REAL dart because it doesn't have either the mass or the front of center designed for penetration.
That's a very interesting way of thinking. Being very much a newbie, I would be more inclined to look at it more like a missile than a dart. Instead of weight forward, you have a projectile that is well balanced and therefore would be easier to tune and more consistent in flight. Obviously gravity and frictional forces (aerodynamics) would be the same (given the arrows have the same overall weight). Also, would a 125 grain head reduce the impact your fletchings would have on the flight of the arrow, mainly the "spin". Most fletching have a slight helicoil to them to help the arrow rotate, as though the rifling in gun bores puts a rotation on the bullet to make it more stable during flight. If you have more weight up front, that's more mass that must be turned, therefore causing the arrow to turn slower. Don't get me wrong. I haven't done the math on any of this and quite frankly have too much going on in order to do so. I'm more thinking aloud and playing devils advocate.
Actually the opposite is true. When you're talking about the rotational force (torque) required to turn that mass, it's about the diameter of the mass, not it's length. There is slightly more mass but the diameter remains the same so there is negligably more energy required to turn it.
What the hell are you going to shoot those things at???? As Rob said, the spinning really isn't limited, and what you get in essence is a projectile that one the spine is corrected, that will fly wonderfully. The vanes in the rear just stabilize a projectile that is now better prepared for flight because of a better balancing. Remove the tip and nock from an arrow and throw it, and watch it's flight pattern. Now put them back in and watch.... Then just remove the nock and it will fly even a little better. Make sure you put the nock back on before trying to shoot it.... :D The front weight as long as it's not TOO extreme, will lead the arrow, those little things in back become LESS important rather than more...
Sorry, I didn't get to finish my previous post because of a server crash. The opposite of what you're thinking is actually true. When you look at the length of the arrow, what the heavier head does is shift the fulcrum (balance point) of the arrow forward (increasing the FOC), by doing this it increase the length of leverage that the fletchings have and decreases the leverage of the broadhead. This doesn't matter much for field points because they don't have blades to exert force on the arrow. However fixed broadheads are a different story. Their blades act the same as the vanes. This is where decreasing their leverage is important. The higher the FOC the more control goes to the vane end of the arrow rather than the broadhead end. This will allow the arrow to stabilize faster and actually will allow the vanes to recover from the shot and start spinning the broadhead sooner. (The arrow won't spin faster because that is determined by amount of offset/helical, length of the fletching and speed of the arrow not FOC.)
So what would be considered too extreme? My Maitland Retribution has an IBO of 340fps, I have a 27" draw and will be shooting at 65# with a 170-175gr broadhead, or a 150gr head with some weight added in the front. I would like to keep my arrows traveling at 250fps or better, and according to OT2, an arrow weight of 450gr gives me that, with a FOC of 16 - 17% (yes, I'm going for more than the "normal" FOC). I figure my FOBs should be able to stabilize it. Is that what you would consider "extreme" or are you talking even more extreme than that?
That's good to know, since this is my first bow since I was 14y.o. (a couple decades ago). Glad to know I'm on the right track. Now I just need to decide on an arrow and a broadhead, but I think I'll ask those questions in a separate thread so this one doesn't get hijacked. I started out my search thinking about the usual 100gr head, and moved to the "heavy" 125gr, and now I'm looking at 150-175gr broadheads! Oddly enough it kind of follows my philosophy on rifle bullets, also.
