Good to hear from you.
I used to struggle and struggle with arrow choices using the Easton arrow charts (and others). While I like Easton products, their arrow charts really don't quite "cut it" for trad shooters.
If you already have purchased the Axis 340 shafts, then you will just have to give them a try. If nothing else, shoot them for a while, and then if you try 400 shafts later on, you should easily be able to decide which is better.
IMHO, the process of selecting a PROPER ARROW is the biggest single "trick" to getting a trad bow to shoot well. Pick the right arrows, and the rest is all down hill from there (easy).
I'm not familiar with Jim's bows, and you didn't mention if it was a recurve or long bow. That may make a difference.
But . . . my bow which would most closely match your bow is probably my Toelke Chinook recurve. Which is 57 pounds, at about 29 inches. That bow really smokes out an arrow. I bet that the speed of that bow will be fairly close (but not quite) to the speed of yours, given that I have a longer draw.
My Chinook bow shoots Easton Axis 400 shafts GREAT. In fact, to get them to shoot well, I still have to cut them long (30.5 inches), and I also use the brass inserts in them (75 grains). Matched up with a 145 grain head, they shoot "right where I'm looking."
To shoot the Axis 340 shafts out of your bow, I strongly expect that you will have to shoot them FULL LENGTH or close to that, with the 100 grain brass inserts, and a HEAVY BROADHEAD. If you can get them to spine right with that combo, then you are in business. Keep in mind that proper SHAFT LENGTH with carbons is crucial to finding the right one.
Try them out with bareshafting, and then you will know if they will work. If you have to use more than a 200 grain broadhead (with the 100 gr inserts), I would say the shafts are just too stiff.
Just for kicks some day, ask a friend to loan you a fletched 400 carbon arrow to try. Myself, I am betting that when it is all said and done, a 400 spine arrow will make you a better archer.
It seems to me that the best rule of thumb when bareshafting is this: IF YOUR ARROW HITS TO RIGHT OF YOUR TARGET AT 15 OR 20 YARDS, THE SHAFT IS TOO SOFT (if so, cut it down, or reduce the weight up front). And, unless you have truly shot an arrow that will actually do that (shoot too far right), you may be settling for overly stiff shafts. In other words, experiment a bunch until you have really experienced OVERLY STIFF and OVERLY SOFT shafts. Once that has happened, the answer (the perfect spine)should be staring right at you.
For years, I used to shoot overly stiff arrows, which is a mistake.
On the other hand, shoot a proper arrow (maybe Stu Miller can help too) and the results will immediately put a smile on your face! The first time I shot the VAP 500 shafts which I picked out with Stu Miller's help, I COULDN'T WIPE THE SMILE OFF MY FACE. Perfection!
Hope this helps. If you need to, many archery shops will sell SINGLE ARROWS, which will probably be flectched with plastic vanes. For a few bucks, buy a single Axis 400 shaft, strip the vanes off, and do some testing with that some day. Then you haven't wasted a bunch of money (and you really need to try them as bare shafts first).
Most guys will say to shoot a bareshaft which shows just a tad bit of softness (shooting to the right), and then flectch that baby with 5 inch feathers (4 inches will work too), and then you have probably found the IDEAL ARROW.
Hope this works. Have a good week.
I say to use 4 or 5 inch feathers. Don't worry about the extra FOC effect from 3 inch feathers . . . that is a very minimal effect that you would receive from that. All of the other factors here are more important (point weight, arrow length, etc).
Jeff in MT
PS -- Send a note here to PLENTY COUPS too (Kent is a real arrow expert, and he can help ya also).