Lordy, ikillsdeer, you really are confused...

First off, there is no such thing as arrow spline. Spline is what you find on gears. When you're talking about arrows, it's arrow SPINE. As most archers use the word, spine refers to the stiffness of the shaft and hasnothing to do with arrow weight or durability, at least not directly.

Spine is generally measured by hanging a weight on the shaft and measuring how much bend, or deflection, the weight causes, in thousandths of an inch. Some shaft manufacturers use the deflection number as the shaft size. Like some Easton shafts, a 340 has a .340" deflection and a 400 has a .400" deflection. The 340 doesn't bend/deflect as much so it's stiffer. The lower the number, the stiffer the shaft.

Not all manufacturers use that system, and even the ones who do use it usually don't apply it across their entire product line. So it can be awfully confusing even for experienced archers when switching from one manufacturer to another, or even switching to different models from the same manufacturer. It sux, basically. [&:]

Most manufacturers list the grains per inch weight of their shafts. That's where the 9.9 or 10.0 typenumbers come from. A shaft that's 10.0 grains per inch is 300 grainswhen cut to 30". Then you add the insert weight, fletching weight, tip weight and nock weight to get your total arrow weight. Anyway, those numbers are simply weight and have no bearing on spine or durability. Again, not directly.

In fact, there isnothing in an arrow size that will tell you how durable it will be, at least when talking about carbon arrows. You can get a good idea about arrow durability when looking at the sizes of aluminum arrows, but, since you're confused enough as is, let's not worry about THAT for now. Generally, the heavier the shaft, the more durable it will be. But not always.

Now, about the 350 grains... Nearly all bows these days are designed to be used with arrows as light as 5 grains per pound of draw weight. So, a 70 pound bow would be in warranty as long as you never shoot an arrow less than 350 grains in total weight. While some dingalings seem to think 5 grains per pound is the recommended arrow weight, it most definitely is NOT! 5 grains per pound is simply the minimum arrow weightthat will keep the bow in warranty.

So, if someone at a bow shop tells you that you need arrows that weigh 350 grains for a 70 pound bow, I'd really suggest you turn around and go to the next shop down the road. As you leave, running out the door and screaming in sheer terror is optional.

If, on the other hand, he was suggesting you get the SIZE 350 shafts as the proper spine for your bow, then that would be something entirely different. Since I don't know your draw length, arrow length, performance level of your bow, release type, tip weight, etc. there's no way I could advise you on that. They all play a part in determining the proper spine arrow for your bow.

Unfortunately though, Easton doesn't offer the FMJ arrows in size 350, so I don't know whether the guy at the shop was selling you a bill of goods or you just misunderstood what he was telling you.

Hope I haven't really muddied the waters for you.