Wood arrows: losing spine?

[slowbowjoe]

Checked the spine on my arrows recently (Doug Firs) and measuring on the same Ace spine/spin tester, find most of 'em are
about 5 pounds lighter spine than they were when I first made 'em up. I don't really have one to serve as a reference at this point, so I'm not sure whether I'm "shooting out" some spine, or if the calibration on my Ace somehow got messed up.
I'll note that a lot of the shafts have taken hard hits stumping, and target arrows have impacted the backstop ( wood or cow mat ) a lot as well.
What do you think?

[Sharpend60]

Self bows can get tired.
I dont see why wood shafts are any different.

[snag]

Are you careful to check the spine against the growth rings each time and not with them one time and against them the next?

[slowbowjoe]

Yup, checking consistently against the grain.

[Stumpkiller]

I've never noticed that with P.O. Cedar or Douglas Fir and I have arrows dozens of years old.  I have one group of D.Fir that has been shot every day for over two years.  I just checked and they are still where they were when new.

[rkelly]

just a thought slowbowjoe when pulling your ars from a firm target pull straight back i think any twisting can weaken the fibers in the shaft

[bigbadjon]

Will moisture content change an arrows spine?