There is more to this story. Those arrows are too stiff for SOME longbows. In this case, I am adding that the amount of cut in the riser will change the whole game. If that bow was cut past center to the point of being center shot (and you said the arrows were cut, but I may have missed how long they were cut to, that matters), it will likely take a much stiffer shaft than one that is not even close to center shot.
I have an RER longbow ( 63#) that is cut to near center and it can have only limited weight on the front of .340s to bare shaft, while another bow, an ASL ( 57#) is not even close to center cut and it bare shafts perfectly with .500 shafts, a 50 gr insert and a 175 to 200 grain head.
A lot of things are at play here for you to understand.
ChuckC