ya the arrow with 75gr. 500spine at 28'' draw 49pounds, weighs 303gr. tried 100gr tip and the bow was untuneable and tore paper terrible. not enough poundage to shoot 400 spine.
If you increase point weight, it can weaken the spine, requiring a stiffer shaft. The poundage isn't the problem with spine. I have a 50lb longbow and I shoot GoldTip Traditional in 55/75's (400 spine) out of it. I also have 210 grains of weight on the front between the insert and the head. Then pin nocks, wraps, and feathers on the back. They total 542 grains.
I can plug all your info into my spine calculator later and tell you what's up, if you want. The more info the better. Bow make/model, weight, draw length, ibo, weight of anything on the string, like silencers, peep, loop, etc. Also arrow model, length, spine, insert type & weight, point weight, fletch type & weight, nock type & weight, wraps or not, footing or not, etc.