I need to set up some arrows for my new bow for the next season. I will be shooting a Prime Rival at around 70lb with a 29.5" DL. I have on hand some Cabela's Carbon Outfitter 340's that I've used in the past and found pretty decent. At their full 32" length they weigh in at 350gr. I considered leaving them uncut and using a 125gr broadhead, which would bring me in at 475gr, right around where I want to be.

I've been told this may leave me under spined, and to rather shorten the arrow a couple inches and add a brass insert. Certainly an option, but adding weight up front softens spine so would I be any farther ahead? I've always cut the arrow to be just ahead of the rest a bit, just because thats the way I've been told to do it but does it really matter if it extends beyond the grip an inch or two?

Shortening your arrow shaft length should increase the spine of the arrow.

That said, I'd invest in different arrows for hunting. I've shot the Cabelas 340s over a Prime Shift and Centroid in 29.5 inches. The arrows weren't that consistent for me, YMMV.

I found 2-3 out of a dozen that would "fly" an inch or more different from the rest. I had not planned on numbering arrows, until I shot the Cabelas arrows. After I numbered the arrows, it was easy to see that the same arrows were continuously grouping different than the rest. They also lost the finish off of the shaft much faster than other brands I had.

You didn't mention your arrow rest which probably mounts behind the riser above your hand. Which means you arrows can probably be cut back a full 2-3 inches and still be safe on your arrow rest. That will change your arrow spine in charts.

There's several different ways to get to the 475 grains you want. But I'd spend some time in the arrows charts. Take a look at what you can safely cut your arrows to for length to get the spine stiffness. You may find that it's easier to go with a heavier arrow than just adding weight up front. I'd regulate the Cabelas Outfitters arrows to stump and squirrel duties, JMHO.

Black Eagle Deep Impact 300 would be my reccomendation. These are a .166dia arrow. Available in 001 straightness. Have a 60grn(approx weight) SS outsert available. Super consistent arrows. And youll reach target weight easily.