Arrow setup question

[builtbybama16]

Hi everyone. It was briefly touched on in another thread but I figured I should dedicate a thread to this topic on its own. I’m looking for suggestions on some new arrows. I have a couple of options (head and insert weight) but what I’m leaning toward is the easton axis 300. I was shooting the 260 but I’m looking to shed a little weight and a little more forgiving spine. Here is my setup and the breakdown of the components. I’m wondering if I should use 100/125gr head and whether or not to use a brass or standard insert. I could probably have worded that a little better but here we are.
Mathews v3 31 at 28.5in draw at 75#
arrow cut to 29”
Shaft is 310.3gr
Vanes 18gr
Lighted Nock 20gr
125gr head and 50 grain insert = ~523fw
100gr head and standard insert = ~464fw
100gr head and 50gr Insert= ~498fw

 

[Rob5589]

#3

 

[Mighty Mouse]

Charts show a 300 spine being borderline weak at 29" arrow length and 75# draw weight. I'd recommend sticking with your 260's if you're wanting to use heavier than normal heads/inserts. Better to be a little overspined than underspined.

 

[builtbybama16]

Thank you guys. What’s the determining factor on insert weight other than FOC?

 

[A-bros archery]

My preference has always been to use 100 grain points and heads and add a little weight with the insert if desired. I guess my reason is simply that 100 grains is a little more common but that's not much of an issue these days with wide availability of 125 grain heads. I think it comes down to personal preference. Will you want to reduce arrow weight or stiffen your dynamic spine in a future setup? If so than go with 125 grain heads so you can loose a little weight by going to 100 if you choose. Might you want to add arrow weight or weaken your dynamic spine in the future? Then go with heavier inserts and you can add weight later by going to 125 grain heads. I didn't do any research but I would also have guessed that the 300 spine would be almost weak at your specs. You could easily cut the shaft a little shorter without any trouble. Remember that bow draw length is measured to the grip throat +1.75". You can have the arrow cut to the same measurement as your draw length or slightly shorter and still have the broad head out in front of your hand. I know you didn't ask for opinions on that but I thought I'd mention it for whatever it's worth.

 

[Mighty Mouse]

Thank you guys. What’s the determining factor on insert weight other than FOC?

I like to beef up the front end of my hunting arrows with a steel or brass in/outsert (or insert with external collar), which is quite a bit heavier than a standard aluminum insert. I do this to improve the structural strength of the front end of the arrow, not necessarily to add weight. If I want more front end weight, I add stackable weight screws (Gold Tip FACT weights or similar) behind the insert. The importance of FOC often gets overemphasized; I build for a target total arrow weight and let FOC fall where it may. If you like to tinker, use heat reversible glue (aka, "hot melt") to secure your inserts so you can easily swap inserts/weights and try out different configurations.

 

[roosiebull]

Thank you guys. What’s the determining factor on insert weight other than FOC?

you may want to cut an inch off of your arrow, then go with the first option. at your draw length, a 28" arrow will be fine and you'll be right in the sweet spot without spine being a potential issue. i'm shooting a very similar arrow that ends up at 524gr out of my mach 1 @ 73# @ 28.5" draw length. i think my arrow is 28 or 28.5" C-C. no animal will know the difference between your options, they should all be a solid option with plenty of horsepower.

 

[builtbybama16]

so I guess after the information I’ve been given my next question is what the insert weight has to do with the spine? I’m getting differing opinions on what’s too weak or too strong since I’m in the middle of the two. I know Mighty Mouse said 300 was weak at 29” but I actually shoot a 28.5” draw length. The biggest difference that has me concerned is my vertix is faster with those same specs than the v3 31.not by much but it is. It’s only one FPS but thats also ibo and eastons chart calls for ATA. I’m still leaning toward #3 in my original post but going slightly shorter 28.5 if you guys think that will work with the additional FOC. I’m just looking for additional understanding.

 

[Mighty Mouse]

so I guess after the information I’ve been given my next question is what the insert weight has to do with the spine? I’m getting differing opinions on what’s too weak or too strong since I’m in the middle of the two. I know Mighty Mouse said 300 was weak at 29” but I actually shoot a 28.5” draw length. The biggest difference that has me concerned is my vertix is faster with those same specs than the v3 31.not by much but it is. It’s only one FPS but thats also ibo and eastons chart calls for ATA. I’m still leaning toward #3 in my original post but going slightly shorter 28.5 if you guys think that will work with the additional FOC. I’m just looking for additional understanding.

Insert weight has the same effect as broadhead weight (or any other weight added to the front end of the arrow): it weakens the arrow's dynamic spine and requires a stiffer static spine to compensate.

Per Easton's spine chart instructions, you would add 5# to your draw weight for a 342 fps bow and select from the chart accordingly. For a 29" arrow at 80#, their chart recommends a spine of 240-260 (Edit: Easton also says to add 5# if brace height is less than 6.5", so you should be selecting for 85# which is technically "off the chart" but close enough to the 79-84# group). As you alluded to, you probably have room to shorten your arrows by an inch or more, which could make a 300 spine workable with "standard" weight front end components (100 gr head and ≈12 gr insert). But if you start adding additional weight to the front, 300 spine might become too weak even at 28". Easton recommends adding 3# of draw weight per extra 25 gr of point weight when using their chart to compensate for the weakening effect of additional front end weight.



All that said, spine charts are just a starting point to get you close and don't account for all factors (such as the additional rear weight of a lighted nock, which stiffens dynamic spine). You'd need software like Archer's Advantage or Pinwheel to get a customized spine recommendation for your particular setup. 300 spine is probably close enough that you could get it to tune well in any of the three configurations you're considering, even if the charts/calculators say 300 is marginally weak. I don't think there's any significant downside to an "overspined" arrow with a compound bow and purposefully err on the stiff side to avoid any potential tuning issues caused by being underspined, but to each his own.

 

[builtbybama16]

Thank you. That makes a lot of sense now. I thought it was likely the same difference because it seemed to me like weight would be weight whether inside or outside of the arrow but you don’t really know unless you ask. It makes a lot more sense that the front or the back would matter more. Since I have so many 260s I’m going to give them a try first and see how they do. If they work well then I’ll keep with what I have until they are gone. If they don’t I’ll give the 300s a try. I’d like to not have to spend additional money for something that I may or may not need.