The spread is the inconsistent speeds of the factory ammo so at 22" length there were chrony readings 103 fps seconds different between highest and lowest so they averaged the 5 shots.
The rifle was cleaned and crowned identically after every inch cut off.
There were lots of sites where 19 inches for the .17 was the fastest fps measured and a good spot if looking for peak fps.
For say 16" which is 6" shorter than current 22" with no loss in accuracy (due to possibly getting a better crown than what,s been done)
25 Fps loss of speed for the round with lets face it , say max range of 200 to 250 in no or f all wind should be fine is really the question
Or is that a huge difference which could cause problems ? Suppose I m unsure of what changes in fps mean but this is a small one ..
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