which arrows?

To explain spine, without getting you lost in the weeds, is basically the stiffness of an arrow. The lower the number (.300 spine compared to .400 spine) the stiffer the spine. When an a bow's energy is transferred into the arrow, the shaft absorbs that energy. How the arrow recovers from that transfer of energy depends on the spine (stiffness) of the arrow. There are all kinds of videos on the web that show this transfer of energy in slow-motion�your arrow actually wobbles as it comes out of the bow.

To answer your question, it really depends on how old is older. The older bows do not have the energy that the newer bows do, therefore will not need as stiff of a shaft. Without having any information, other than what was given, I would go with a shaft that has a spine rating of .330-.350�it is better to be slightly over-spined than to be under-spined. If you can provide the name of the bow, we may be able to zero down that year a bit and get you closer to a more exact answer.
 
From the information I have...your spine match is around .370. The problem is that no one makes and arrow to that spine, so the best thing you can do is to go with an arrow that will be slightly over-spined�use a .340 spine arrow.
 
Generally the rule of thumb is to have the end of the arrow shaft 1" past the rest, but sometimes you can manipulate arrow length to achieve an ideal spine match, if your close to an ideal match. In your case, you're not close to match�you're almost perfectly in between spines, so just have a .340 spined arrow cut 1" past the rest and you will be fine.
 
Tndeerguy speaks the truth! The only other factor is broadhead weight. Contrary to popular belief the 400 spine on the average arrow shooting a 100 grain broadhead is only good to about 62-63 pounds. I really think about half the "tuning" issues on here are actually arrow spine issues. All that said I shoot a 400 spine because I see no need to pull anything over 60 pounds...... then again I still shoot feathers and line my broadheads up with my feather too!
 
To complicate things you can shoot a 125 grain head to make the spine weaker. If you put a 85 grain head the shaft becomes more stiff. Personally I shoot a stiff spine for my set up with great results.
 
A PSE Pulsar?? That was my first bow.....still have it actually.
 

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