With a Helim at 30" and 70#, I'd likely go with a .300 spine, those 350's are actually only a .340-ish spine, and you need about 29" of shaft, which means you need an even stiffer spine yet than someone shooting a 28.5" draw because you have an extra 1.5" of build up energy behind that arrow. Put a fixed blade head on the end of an arrow and you'll see how far off that spine really is... Also out at a distance you're gonna find that those arrows tail off a LOT if you're really shooting 70# and 30" with a light .400-.410 spine shaft... Right fliers will be the common problem the longer the shot the worse the flight gets... That said, I shoot a Hoyt Alphaburner at 29" and 62# and shoot a .320-ish spine arrow and load the front with a 125gr BH and it's still a tiny touch toward the weak side according to OnTarget2, but not enough that I don't get decent flight out to 40yds. Consider the Alphaburner is a 340 IBO bow vs. a 332fps IBO rating out of your Helim (but you're adding an inch of DL, therefore the energy of both bows is likely very similar at same weight), now add the extra 8# or so, and you're definitely getting down to where a .300 is the more optimal spine. Not on my computer with OT2, but there are certain specific general set-ups that I'm usually pretty close just off of my head on, and yours is one I'm sure of, but TFox can likely give you better spec's as he's probably more knowledgeable about this topic than 99.9% of the members here...
Thats interesting. My arrows are 29.5". So you're statement rings very true. The weird thing is how accurate the bow is even at 50 yards. I just started using a react sight so I was testing the 50 yard pin. It was still stacking them. That's why hesitant to switch as was mentioned above your comment. I did have an arrow break in the middle during my last practice session though. That concerns me.
I like a heavier arrow myself. I used to shoot the maxima blue streaks the 350s and now I'm shooting fmj 400s. also new for this year I switched to 125 gr g5 strikers. I really like that combo. Shot a mountain goat in August and a black bear in May. Pass thru on both and dead quiet at the shot. I really like the heavier set up I'm using this season. My blue streaks were faster but didn't penetrate nearly as well. Like stated in the other comments if think with deer you shouldn't have a problem shooting any kind of arrow light or heavy. But myself going on an elk or moose hunt I'd rather have a quiver full of heavy arrows.
