I'm shooting a 3 piece pronghorn longbow 63@28 and I draw 27". No strike plate. I'm shooting 29.5" Goldtip trad 5575 with 300gr up front. They seem to shoot well, but the calculator says I'm way under spined. Is this so unbelievable a setup? I shoot 3 under gap and the arrows hit straight over the point, no left or right movement. Although, I do see a fishtail on a bad release.

It has been my experience,when talking about higher FOC arrows,the calculator doesn't work real well and always says they are weak when the aren't.

Jim, thanks for the reassurance. I was getting a little worried after a few bad practice days. I just gotta quit out thinking my self I reckon.

Same here ,I am 60# @ 28" r/d longbow . I have been shooting 70-75's (poc) @ 29" BOP , 125gr woody weight and 160gr heads. The calc. shows ths to be way under spined also. I think it boils down to what flies well and shoots quiet. These arrows are heavy (720gr) but they fly awesome and the penetration is solid.

Glad to see I'm not the only one. Mine weigh right around 590 grains. Very solid arrow compared to what I'm used to.

Same for me ...the calculator does great with aluminum arrows shooting 100 - 175 grains up front.  I've never had it work for carbon arrows.  In fact, it typically hasn't even been close.  Learned my lesson the hard way by trusting it and cutting some arrows leaving them WAY too stiff.