Gardner's mass theory and 100# + bows

[JNystrom]

I have been thinking this for sometime and i think this is better place to open a conversation than the FB platform.

In TBB4, there is a superb section about Steve Gardner's mass principle, which shows you how to track a proper mass for your bow is it a longbow, shortbow, perryreflex, ipe or juniper. With this mass table, there is some extra rules to get finer estimates including this one:
"On the ELB designs calculate them out as normal and then multiply the answer by the following factors: 100# X 0.90, 90# X 0.92, 80# X 0.94, 70# X 0.96, 60# X 0.98."

First of all, where does this -10% mass on 100lb elb come from? Will the factor be even lower when you go over 100#?

There is one australian guy in fb group that i conversated with about his 75" osage warbow, which is quite heavy in mass for its poundage which made me think the mass principle further. He is aiming for a 150# @30" and the mass for this kind of bow should be around 37oz (1050g), while many of these to-be osage warbows of different bowyers are whopping ~50oz (1400g).

[JW_Halverson]

I get the feeling that a badger is coming along any minute now....

[JNystrom]

More thinking: could it be that the unordinary length of elb somehow lowers the projected mass? Or is there some updated view on this...
Would be nice if Mr. Gardner could share some dimensions and mass of his self made 100+ pound bows.

[Badger]

  The mass theory could use a little work in the heavy longbow dept but still surprises me how accurate it works out. It was not really intended at first to project out past about 80# but I have been using it with regularity up to about 120#. On the extra long bows which I don't make a lot of I think it tends to add a bit too much mass, most of mine are 74" and under. Yew bows also tend to do better a bit lighter like 10% or so. As for osage, I have only made one really heavy osage bow and it was a slug, I think it was 150# and about 76" long, it should have come in about 38 oz and came in at 44 oz. It didn't take any set and I could not test shoot it but the early weight was surprisingly low and it was quite easy for me to brace. I can't normally brace a bow that weight and length without using my jig I have set up. I chalked it up to the wood not being dry, I ended up cutting it into a regular stiff handled 50# bow and it was fine.

[JNystrom]

What is the method to estimate the mass of over 100# elb's? What factor do you use? Just that 0.90?
Have you figured out why elb's tend to come out lighter in mass?

Seems interesting that yew elb would be 10% less in mass, well we see how favorable yew has been for longbows for ages.

[FilipT]

I used the calculator when making my first warbow and it was really precise. I missed the mass by small number of grams/oz.

[Badger]

  The reason it is off is simply because the formula was developed as a rule of thumb rather than an absolute scientific calculation. It was developed around 50# to 60# bows so I was actually pleasantly surprised when it didn't not run off more than I thought it might when getting into heavier poundage's.

[JNystrom]

Seems like i'll do testing of my own! I have a elm bow, 72" and 110# at 28", it weights now 818g (28,8oz). It took set of 2" so maybe i should heat treat it and tiller it to 120# @30". Or just shoot it at 29" and 115#... Seems like the mass is about the same as projected with the mass principle without any elb reduction factor.

Badger:
I happened to read about warbows from paleoplanet, especially Jaro's, when i tumbled on this:
https://www.tapatalk.com/groups/paleoplanet69529/viewtopic.php?f=46&t=10628&p=10285#p10285

I guess this is the osage warbow you were talking about? Still some pictures left.

[colin1991]

I'm the Australian chap that made that Osage warbow mentioned earlier.  The bow ended up coming in at 180# at 30" and its mass is in the vescinity of 1450 grams.  No idea what the mass principle says but it's near impossible to brace alone and i am yet to shoot it but the early weight is ridiculous.

[Del the cat]

First a disclaimer... I don't use the mass theory.
BUT.
I'd have thought it should be nicely applicable to Warbows as they are virtually all working limb with no dead weight or add-ons like riser sections etc.
I really should weigh some and do the arithmetic, but it's just not my bag ("bag"= "lazy git"  ).
An interesting tool and concept tho' 
Del

[leehongyi]

I have been thinking this for sometime and i think this is better place to open a conversation than the FB platform.

In TBB4, there is a superb section about Steve Gardner's mass principle, which shows you how to track a proper mass for your bow is it a longbow, shortbow, perryreflex, ipe or juniper. With this mass table, there is some extra rules to get finer estimates including this one:
"On the ELB designs calculate them out as normal and then multiply the answer by the following factors: 100# X 0.90, 90# X 0.92, 80# X 0.94, 70# X 0.96, 60# X 0.98."

First of all, where does this -10% mass on 100lb elb come from? Will the factor be even lower when you go over 100#?

There is one australian guy in fb group that i conversated with about his 75" osage warbow, which is quite heavy in mass for its poundage which made me think the mass principle further. He is aiming for a 150# @30" and the mass for this kind of bow should be around 37oz (1050g), while many of these to-be osage warbows of different bowyers are whopping ~50oz (1400g).

what is the unit？gram or oz? And the draw length?