Is there a guide for x number grains decreases spine by?

[Archer1019]

I have some full length vapor shafts in a 400 spine with 125 gr points. They appear to read stiff fom my bow. Will 15 grains to the tip (via brass washers) make enough difference to change the spine? I say 15 grains since 3R notes the most to use is 3 at 5 gr each. Looking to see if I ought to just start with heavier tips then add the brass washers.
Thx

[Skipmaster1]

I've found that with carbon arrows, it takes a lot of weight to effect spine where a small change in length makes a pretty big difference. I usually start full length with a heavy head, making the spine a little too weak and then trim a little at a time to get the spine right. It all depends on what you want for a finished arrow. I'd try brass inserts and a FP test kit to see what combo works for you

[Biathlonman]

25 grains seems to net be about 5 lbs. less spine.

There is no chart. Every different brand arrow that says".400" on it is different from each other, and probably none are exactly .400 spine!

Also, each spine class, .400,.500, etc are different stiffnesses and each would require different #'s/# of difference made.

15gr will not do much to change anything unless you are right at the edge anyway. I use the brass washers (I only use one) because my field points are 145gr and my broadheads are 150gr. I like everything to be the same, and 3Rivers sells them, so I use them. I have tried to put 3 on at one time before while experimenting with setups, and I did not like it at all. With 3 on, if the head starts to back just a little, you can lose it all when it falls off.

Bisch

[Trond]

Agree with Skipmaster1. I have tried both 125and 100 grain up front on GT1535's and can't see any significant difference. That said, my 125gr has 5" feather while the 100gr has 4". Bigger feathers also affects dynamic spine.

[ozy clint]

FOR ME, with axis shafts with 350gr up front out of my 58# border recurve i found during tuning that 1" of trimming equaled 50gr of point weight.

eg- if i trimmed my tuned arrow 1" i'd have to add 50gr to the front to be tuned again.

[Bladepeek]

I think if you experiment a bit with larger point weight changes that you will find, as several posts above point out, that large weight changes or small length changes will have similar effects. Since the arrow is already a bit too stiff, changing the length is not an option. I would get some points that are significantly different in weight - like, 145,175, 200. That might be enough to move the arrow over to the weak side and then you can work your way back to tuned. You didn't say what bow weight your shooting, your arrow length and draw length, or how stiff they appear to be, so you might be very close, or so stiff that even a 200 gr point won't do it. It would help a lot to give a few more details on your shooting setup. I know if I were trying to shoot even a full length 400 spine out of one of my lighter bows, it would take a LOT of weight up front. Probably 100gr insert and 250 - 300 gr point. On one of my heavier bows, I could make it work quite easily if the shaft is full length.

I know shipping costs are greater than the cost of the arrow heads, but if there is a trad store anywhere near, points are pretty cheap. Also, there are probably some trad archers in the area that may be able to help you out. It takes very little effort to swap out points on a "loaner" basis and see if that will help.

[Archer1019]

As soon as our rain let's up, I'll shoot a few more then post the specs on bow weight, arrow length, point weight and arrow impact fetched and bare.
thx

[olddogrib]

I'd try 175gr.  If that's too much you could back off to 145 gr., but I need about 50 gr. and multiple shots with my "less-than-perfect" to detect a difference.

[Archer1019]

OK, got out in between rain drops and things were not as bad as initially thought.  I really focused on a clean and as consistent release as I could and appear to have improved. It seems my initial thoughts may have been impacted by the release and windy day which I was shooting.  I will tinker some more before adding heavier points or changing arrow spine so as to control the variables.  Thanks all for your input!

[Jim Wright]

I only shoot wood arrows anymore and with them 35 grains of point weight affects a 5 lb. spine range. As has already been mentioned, carbons are a much harder calculation, get a variety of heavier points and don't be surprised if that turns out to be HEAVY. If you are way down in the manufacturer's brace height range, you can soften stiff spine a bit by increasing brace height. If you have a thick strike plate you can affect spine the same way by going thinner.

[JRY309]

It doesn't always work that way depending on how the riser is cut and length of arrow.I had some used CE 45/60(.400 spine) cut an inch past my draw.So I thought I could add more weight to weaken the spine.They got worse and showing even stiffer the more weight I added.They were bouncing off the riser instead of flexing around it.I did tune the same spine to that bow from full length shafts and ended up around 2" longer.Now this was on a longbow cut about 1/8" off center.May have worked if I was shooting them from a recurve cut past center.

[katman]

I would increase point weigh to 175 or 200 if you can and see if it improves or worsens, that will tell if your getting an accurate or false reading. If stiff others measures to weaken dynamic spine are to decrease centershot with a thinner strike plate, increase brace height and or decrease mass of the silencers if you have them on. Once tuned the arrow will be a little more forgiving of perfect form. Having several weights of points around will be useful for future bows.

To answer original question it usually takes me at least 50gr point weight to see a change in dynamic spine. No specific formulas I know of due to many variables listed on others posts.