If you would like to know if those arrows are too weak, then back your poundage back about 3 turns on the limbs and see how your groups look. That will tell you much. You can always buy different arrows if the results improve.
IMO, the .400’s are very weak for the 70# Helim…FWIW, Im shooting a 28/60 HeliM with GT XT 75/95’s ( .350 spine) and They papertuned and are grouping GREAT. I bareshaft tuned with these and they showed stiff though….Shoot a bare shaft and see if it hits with your fletched arrows….Im guessing it’ll show WEAK ( hitting left of your fletched arrow).
CHILL 28/70 "BLACKOUT", QAD HDX, Ktech5 twin, HHA XL5519, T3 quiver, Goldtip XT 75/95's, Rage 2 blade Chisel's
Drenalin 28/70 WB, B Stinger,HHA DSXL5519,GoldTip 75/95's, Rage 2 blade Chisel's
Carbon Express has made it easy to select the proper spine for your setup. Several other arrow makers have also made some improved selection adjustments so most shooters can make a better choice in their arrows.
Generally, a .400 spine shaft is weak out of a 70# bow unless the DL is very short (less than 26″), and even at that a 75-gr point weight is usually required. It is possible to tune for bullet holes with FPs with a weak spined shaft IF form is consistent (no bow hand torque, no string or fletch contact with face/facemask), nocks are precisely indexed to stiff side of spine if there is one, spine consistency within the dozen is very good, etc., but even if tuned for FPs, weak spined shafts will not generally group broadheads well, especially fixed-blade broadheads.
Check out OnTarget2 free demo software if you want a more precise estimation of the correct spine, especially if you are using illuminated nocks, wraps, insert weights or insert adapters, etc. http://www.pinwheelsoftware.com/
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