I think Stu's Calculator is really cool and I love "gaming" with it. However, I've done some calculations and what I'm shooting, very well, shouldn't work.
At the recommendation of a friend I obtained Beman MFX Classics in size 600. I bought them without charting and before I had even heard of Stu's Calculator etc. (My friend and his wife are very competent in these matters). The 600's fly beautiful out of every recurve I have -- 43-47 pounds at my draw weight. I've tuned the bow so broadheads and field tips strike the same spot -- I've checked out to 30 yards -- 5 yards further than I will shoot at game.
But, Stu's calculator says this 600 is WAY underspined for my bow.
The Bow: 52# @ 28", -3/16, my draw 26" = 69.2#
The Arrow: Beman MFX Classic 600, BOP-28, point weight 100, insert weight 75, nock 9, 3, 4" feathers.= 50.3 #
Since this 600 is only 415 grains I'm going to bump up the arrow weight next year. Although I have no complaints having passed through 2 lung-shot does this year.
I plugged in the MFX Classic 400 and it comes out at 67.8 # which is much closer to the bow which remains at 69.2.
Do any of you have such discrepancies with Stu's Calculator?
Please don't get me wrong, I'm not bashing the calculator or its author, it probably works well for many but...?
P.S. I'm about to order 2 more dozen Beman MFX Classics. I was thinking to go with 500's, up one size to gain some weight and accomodate a 150grain broadhead - my arrows would be about 485. However, now I'm thinking of getting 400's which would get my arrows nearer to 550 grains.
Most of the time that I've found it to be wrong the stats on the bow were wrong. What bow are you shooting that is 3/16 past center?
Also a lot of guys can shoot lighter spined arrows off of the same rig. My problem is they hit right of where I'm looking even though the test well.
Mike
If you want your arrows near 550 I would try Heritage 150's. You're going to be adding quite a bit more weight up front on those 400's. What Mike said above is on. Most of the time (but not always) the calculator is off because the shelf measurement is not what you think it is. A +1/16 measurement makes those 600's just about perfect.
I get real close on my bows cut to or just out from center some. I mostly shoot LB's. On the recurves cut past center I get a different result. I am shooting the same arrow, that I shoot in two of my LB's, in about the same draw weight black widow PCH. It should be way off, but it shoots great with a bare shaft and confirmed shooting paper. I had the same thing a while back when I had another BW. I also saw this with a predator I had a while back.
One thing I would do is shoot paper. I have seen bar shaft groups look ok and even broad heads look ok, but paper show me weak flight. It has become something I now always do as a double check particularly with HFOC arrows.
this is gonna go against the grain of most thinking and will even raise some hackles, but it's the essence of a LOT of personal testing with a large variety of carbon shaft brands, models and spine ratings.
ok, so, imho, what i believe, and what works for me ...
carbon shafting has a much stiffer dynamic spine than static spine. all the carbon shaft spine charts are far too stiff than they're listed. :readit:
there are some essential main factors to consider - bow holding weight, degree of "centershot", bowstring spex, arrow dynamic spine, archer's form and aiming methodology.
carbon shafting is just in a separate class from alums and woods and glass (remember microflytes?). it has a much broader range of inherent stiffness. i bare shaft alums and woods, but see no need to do so with carbons. as it is, my arrows have minimal steerage and are closer to a bare shaft than most arrows with 5.5" high back 3-fletch heavy helical feathers.
my "go to" longbow is a mild r/d mohawk t/d, 62" and holds a tad over 55# at my 29" draw. i'll add - a full 1/8" proud of center at the arrow plate, including a thin teflon tape strike plate. my hunting arrow of choice starts with a 29.5" beman ics hunter 500 shaft, 350gr up front (100gr brass insert, 125gr steel adapter, 125gr wensel or field or judo), custom low profile 4" banana 4-fletch, classic nocks. total weight is 585 grains and the foc is over 26%. by all the charts, this arrow should be incredibly weak spined for 55# of thrust. one would think.
my arrow flight is like a rocket on rails, as long as my release is at least decent. if the release is rushed and very sloppy, the shaft will still straighten out well enuf for good penetration, thanx to the high foc (which i believe also makes for some measure of increased penetration). i have blown that arrow completely through the body of a 100+# hog @ 17 yards. i don't need no arrow charts or fiddlin' with calculators or playing with arrow weegee boards. the proof for me is in consistent arrow fight - and well killed game.
there are some carbon shafts that require NO thinking - point up, fletch up, shoot. tapered arrow dynamic trads are one such shaft. that one shaft will handle a HUGE array of front end weights and shoot like the dickens out of 45-65 pound stickbows. if yer skeptical, ask me how i know this.
as always, ymmv.
(http://img.photobucket.com/albums/v82/rfdee/archery/snuff1.jpg)
QuoteOriginally posted by Mike Walker:
Hi Roy, try this......
For Arrow Input---leave the 75gr. insert weight,but change footing option to "yes" and 1" length with weight "0".This will compensate for the long HIT insert.
Hope this helps.
Mike
This was posted on here a while bach. If you don't do this with arrows that take the HIT inserts the calculator will be wrong. The internal insert being so long does effectively work as a footing when it comes to spining arrows, which changes the whole game
I often have to experiment with my shelf side plate to get the most out of my arrows, which is why I choose to use slightly weak spined arrows so I can build out my strike plate until I get ideal flight.
Just because your bow manufacture says the bow is cut 3/16" past center doesn't mean it's exactly that. Plus, after you add any material at all to the side plate, it no longer is 3/16" past center but it becomes less than that, depending on what material you use on the side plate area.
I find that the single most important entry used in Stu's calc., and the most critical, is probably the center-cut measurement. It makes a HUGE difference in the outcome.
I have the same results as Rob with my Mohawk. I'm shooting 55# @ 31.5 with Beman ICS classic 340's, 31.75", 100 grain brass insert, 185 grain head, 3 5" shield cut feathers.
Bow calcs out at 56.9, arrows at 48.5. The arrows fly like darts out to 30+ yards. Broadheads, bare shafts, field points all hit together????
I changed the footing option as Rob stated. I also found that the strike plate distance had a larger than expected affect. Vince said it was 1/8" before center but with a piece of calf skin it's more like 3/16" before center. Using 1/8 I get 59.9 for the bow!!!!!!!! The 3/16 closes it some. This makes my form factor -6!!!!!
" The Bow: 52# @ 28", -3/16, my draw 26" = 69.2#"
If your draw is only 26 your draw weight would be about 46-47# ????????
To get 69.2 out of that bow your draw length would have to be 33.7.
Bowmania
QuoteOriginally posted by hvyhitter:
" The Bow: 52# @ 28", -3/16, my draw 26" = 69.2#"
If your draw is only 26 your draw weight would be about 46-47# ????????
He's refering to the Dynamic Spine Calculator, not the actual draw weight of the bow. A bow cut past center will require a heavier spine shaft hence the reason for the adjusted draw weight number of 69.2#.
Got it....but adding 20+# seems a little optimistic for being cut past center to me. I dont use Stu's Calc but just going by the Bow specs I would have said a 2016, subtract 2 inches of draw, 1916. 1916 deflection is .623 so the 600s look like they should be tunable and work.
I have always had some input that is incorrect, because my bare tuned shafts are always about an inch to inch and a half longer than the calculator predicts.
Folks I do appreciate this input. This isn't a post where I have formed an opinion and think I know the problem and am just checking everyone else out -- so thank-you.
I had not considered that insert, which is quite long as having a footed-affect. Makes sense to me. I'll make that change.
The manufacturer did state the Centershot and that's what I'm going by. But (duh) I'm using a springy and my arrow isn't against the shelf so I'm definitely -3/16th so this is going to change things a lot.
Finally, I appreciate the reminder on draw weight change at 26". I know that on almost all my bows (I check with digital scales) that I lose about 3 pounds/inch. The reason I reported the 52@28" and my draw length at 26" is because that's input Stu's Calculator asks for.
My issue was that an arrow that shoots great (the 600) wasn't calculating. Now I think you folks have explained why.
Grrrrreeat!
Son of a Gun!
I just did all you folks suggested. Now I know why the 600s fly straighter than my dog-teasing laser!
I said yes to footing, added an inch, no weight. Left the insert at 75 grains. Then I checked centershot and found that I was at "O". The numbers are 56.3 for arrow and 56.2 for the bow.
Wow, you folks saved me a bunch of wasted arrows and Grrrrrief!
I'll have to find another way to add about 100 grains to the shaft. I know some things I can do, lop off a bit more arrow, install weight tubes, or NOT WASH THE BLOOD OFF MY FEATHERS!
Thank-you!
Now, how about this issue I have with dry wall screws.... I know, I need to find another forum.
now that you have the formula for your bow that works it's easy to build a heavier arrow. Select the next stiffer spine, set up at same length and add insert and point weight until you get 56.3.
Mike
Thanks Mike!
That footing affect will get you for sure as will assuming the center cut. I know when the first couple versions were out I would have problems getting things to shoot right when changing from 100 gr. to 50 gr. insets and then bumping up the point weight. It didn't work due to footing effect unless I fudged the arrow length number to compensate. Even then there is a little something to forward location of the weight that I don't think you can calculate because increases in point weight don't happen right at the end of the shaft. Larger point add their weight further and further forward as you go up in weight.
My latest issue has been shaft diameter. I can't get a Beman 400, GT 5575 and CX250 to all calculate the same and shoot the same for spine. There is a little difference and I think it could be the slight variation in outside shaft diameters between these arrows.
The calculator is a great tool, but I still play it safe and allow some room for adjustment when working with a new arrow set-up.
If you just want to increase the arrow weight of the shafts you have without increasing the foc you can just stuff three pieces of weed whip line in the shaft. Three pieces stuffed in my Heritage 150's (which are cut to 28.5) adds just about 100 grains.