Tuning For A Heavier Arrow

[dcolavito]

Hi Folks

I'm looking to increase my arrow weight from 412g to about 550g for improved penetration with my 55lb bow.

I'm thinking that my "point of aim" will rise, perhaps significantly, though I'm not sure how much until I try.

After thinking more about it, I was wondering whether it makes sense to try and tune for "point on aiming" with the heavier arrow at my hunting distance of 15yd-20yds.

I've never used "point on" aiming, and it seems like it might be more reliable than gapping.

Any advice on whether this would make sense, down-sides, etc... assuming it's even feasilbe.

Mucho grats !!
Dave

[O.L. Adcock]

Dave, Everyone is "point on" at some distance whether they use it or not and what that distance is depends on their physical proportions, where they anchor, 3 under vice split and a dozen other factors besides arrow weight...You can change those variables to change your point on if you wish. Otherwise tune your heavier arrows then get use to them. You are looking at 10gr/lb and my point on is 50-55 yards at that weight and 40 at 14 so as you can see it's a personal thing that no one can answer for you.....O.L.

[Snakeeater]

If you are asking if it makes sense to go up in arrow weight until your point on distance is around 15-20 yds, the best thing to do is to give it a try. Maybe get some heavy points and see how they affect your elevation.

[dcolavito]

Yep, Larry, that's what I was getting at.

Actually, among the different broadheads (150g,190g), adaptors(75g, 125g) and shaft (9g/in, 12g/in) combos I've been looking at, it seems I can end up anywhere between about 9g/in and 13g/in.

In the end, how they fly and good penetration is what matters, but I'm wondering how heavy g/in it makes sense going before reaching a point of diminished returns (irrespective of where my "point on" ends up).

Any thoughts on this are helpful in determining how much trial and error I should expect to diddle with (along with the gelt!).

Thanks,
Dave

[O.L. Adcock]

Dave, "In the end, how they fly and good penetration is what matters, but I'm wondering how heavy g/in it makes sense going before reaching a point of diminished returns (irrespective of where my "point on" ends up)."

There is no "point of diminishing returns". Other then when you get to the point you can't live with the trajectory. Efficiency and momentum continue to go up.....O.L.  

 

[dcolavito]

Excellent O.L..  Thanks again !!

Seems increasing mass is the gift that keeps on giving !

But what about F.O.C.???  Any practical limits there??

I just finished reading Dr. Ashby's evaluation of extreme F.O.C. for a 54# longbow - particularly interesting for me since I shoot a 55# recurve.

And since I'll be evaluating much heavier arrows (about 700g compared with the about 400g I've been using), I'd like to better understand why he chose 25% for the extreme F.O.C. in that work, and whether it's beneficial to go even  higher. Perhaps I've overlooked him already explaining this, so if that's the case, much obliged if you have a reference.

Dave

[O.L. Adcock]

Dave, the Doc considers over 20% as EFOC as that seemed to be where the jump in penetration occured. Before you go up to something as heavy as 700 gr, you might consider the bone breaking threshold seems to be around 650. EFOC's in the 650-700 range penetrated as well or better than 800-1000gr arrows with "normal" FOC's.

That is his next step is testing Ultra FOC's (UFOC's), in excess of 30%...Without taking his thunder but early quick and dirty tests are showing even more remarkable gains. I know aerodynamiclly there is no such thing as too much FOC, it's all a matter of how to do it when comercial parts are not available and getting the bows to tune to them...Fun stuff!   ....O.L.

[dcolavito]

Fun stuff indeed, O.L. - can't wait for the UFOC results.

All things being equal, one would think that continuing to increase the FOC should result in progressively weaker spine, thereby possibly driving the need for a stiffer (and likely heavier) shaft (at least for me, since I'm shooting aluminum), which would then in turn cause FOC to subsequently decrease - unless shafts are shortened, to at some point, the limitation of draw length.

I guess that's the value of Doc's outcoming oriented work - to separate reality from what we "think" will occur.

Thanks for the suggestion of backing off a bit to about 650.  I just figured going to something like 700  would put me "firmly" into the bone-breaking regime. Of course, I'll have to see what trajectory is like, but hopefully I'll find a good operating point somewhere above 650.

That's part of the reason I wanted to give the Doc's Griz 190's a try - and also, since he's characterized them so well in his work.  So given the imporance of structural integrity - (I'm interpreting that as a need for steel adaptors and inserts -the new shafts that I'll need (will have to experiment, but I'm guessing 2117's) could limit how 'low' in weight I can go......we'll see.

Dave

ps. Having some trouble locating steel inserts...any toughts?

[O.L. Adcock]

Yep Dave, aluminums are an area we haven't played much, mostly carbons and woods. The spine and stiffness don't follow "weight" directly. They all gain stiffness by the cube of their diameter so the trick is going a bit fatter (as long as it's less the the point) with thinner wall and or moving away from centershot more. If a person has a bow that's close to center and goes up in point weight till it "tunes" and if it's as short as they can get away with, that's as far as they can go. Start moving the side plate away from center and you can continue going up in point weight. I'm certain there are limts for any given combination. That structuraly integrity thing...Got to be footed but footed internally, not outside and in a way that doesn't simply move the weak spot to another place. Have no clue on steel inserts but do have a source for tungsten!   ....O.L.

[freefeet]

How does one add weight to the front of a wood shaft with a broadhead on it?

For example, if i were to have a 125gr woodsman on a wood shaft and wanted to make the front heavier is there any way i can do that keeping the 125gr woodsman on the front or do i have to get a heavier broadhead altogether?

Sorry if this is a silly question but i've only recently started playing with arrows.     :D

[O.L. Adcock]

Freefeet, Heavier broadhead is the easiest way if it's enough. I made a jig to drill a 1/8" or 3/16" hole in the center of the wood shaft tapers about 2" deep. I can then use brass, steel, or tungsten rods of varying lengths for more weight and or tuning adjustment.   ....O.L.

[Dozer]

O.L. since we're talking about FOC I was wondering if there is an arrow that would have a stiff enough spine to handle 300+ grains up front yet still be light enough to keep the weight around 600 to 700 grains. I'm looking forward to the Doctor's results on this UFOC test and how he got the weight up front without shooting rebar for arrows.

[O.L. Adcock]

Dozer, I'm shooting Stikas out of 47 pounds or so with a 160 head, 125 adapter, 75 gr insert for 360 up front and total arrow weight is 650. FOC is 27% if I remember correctly.

The UFOC's will be similar to that above with 1-2" of 3/16" tungsten behind the insert with a 60-70 gr internal wood foot for 6" or so. The tungsten weighs 130gr per inch! The internal foot will help stiffen the arrows a bit from all that weight up front. Not sure what arrows he got but I think they are gold tips in 75-90 to be shot out of a 75# bow....O.L.

[dsa1817]

Speaking of spine, I've been playing around a bit and I found something interesting.  I thought for sure I'd need CX 350s for what I wanted, but here's what I have so far.  CX 250 @ 31", 295 gr. head, 100 gr. insert.  395 gr. up front, total arrow weight at about 750 gr. or so and about 25% FOC, I think.  Out of my 65# Martin ML-14, they fly great.  This sounds horribly underspined, but they fly pretty well, at least out to 10 yards.  I haven't shot them out further, yet.  I don't have any way to confirm my draw weight, but my draw length is 29 1/2".

I'm afraid to mess with it any more, coz my groups look pretty good (to me, at least).  Maybe my bow is actually a lot lighter than marked, but it's heavier than my 57# Jeffery's recurve. I only tried this combination coz the same arrows with 145 gr tips and alum inserts (which shot great out of the recurve)were hitting way left.  So, either I've stumbled onto something good or I'm doing something WAYYY outta whack.  Any thoughts?  Because I can't understand it.

Umm, I don't think I'm hijacking this thread (I'm not quite sure what constitutes hijacking), but if I am, I apologize in advance.

[freefeet]

Thanks O.L.  Adjusting the up front weight makes sense now.

   

[O.L. Adcock]

dsa1817, You can take that bow and build the side plate in or out and you'll need a completely different set up. You may find that to be the case as you start shooting at further distances also. If the "350" is a deflection designation, that's 75# and well within line of what you are shooting and possibly even overspined. The only reason you'd be getting away with it is because of so much weight up front. Don't try to make sense out of what you see between 2 bows, just because the Martin is 7 pounds heavier then your recurve, odds are it's not putting any more horsepower into your arrow then the recurve is plus it's probably a lot further from centershot....O.L.

[dcolavito]

O.L., I'm a neanderthal, stuck in aluminum land, what are the "Stikas" you were referring to above? (wood, carbon ?)

Thanks,
Dave

[dcolavito]

I've been looking at the carbons, and unless I'm confusing myself, I'm getting absurdly high (computed) FOC's with the Griz 190 and steel adaptors (either 125's or 75's)for my draw (28 1/4)

I'm estimating using (BP/SL - 0.5)x 100, and 'assuming' the Balance Point (BP) is that point along the shaft where the weight of everything "up front" plus whatever additonal shaft is needed, equals the weight of the remaining shaft+nock+fletch.

I know this estmating approach significantly "underestimates " measured FOC, since I've cross-checked it with my existing aluminums.

You can try this using 10gr/" for carbon, 190gr BH,75gr adaptor, 25gr insert and 28" total shaft length, and 15gr for fletching and nock. With this configuration I'm getting about 50% FOC (190+75+25)=290 up front, vs. 280+15=295, so BP would be about 1/2" behiind the head, yielding an estimated FOC of about 50%!!!

Anyway, reason I'm getting into all this is I'm trying zero in on the best carbon prospects for proper tuning (since I've only used aluminums)with my 55#/28" draw recurve. I realize there's significant trial and error involved, but hopefully I won't have to sample every carbon shaft option !!

Much appreciated to those who can save me from myself !!

Dave

[O.L. Adcock]

Dave, "Sitka's" are carbons from Alaska Bowhunting supply.

Where did you get that formula?    Coming from the aviation world the way the archery world measures balance point is odd. Measure your shaft and mark in the center. Now balance the arrow and mark that point. Measure from the balance point to the center...Now divide that by the shaft length. A 30" arrow that balances 3" in front of center is a 10% FOC.....O.L.

[dcolavito]

Thanks O.L.

That forumla I use is really the same one you use.

Using your example:

SL(shaft length)=30
BP (Balance Point)= 18

FOC=(BP/SL - 0.5)x100= 10%, just like you say !