Thread: 22lr barrel length

Okay, I will assume this topic has probably already been covered .
That said I was checking out some charts today re barrel length vs velocity as I am considering cutting the 16in barrel on the papoose down to 14 inches .
But after checking out the charts I am now thinking 13 inches .
And something else I had never considered when perusing these charts is semi vs bolt action .... as the bolt stays closed for full length of barrel travel in a bolt action , giving a backstop to barrel pressure but a semi opens the bolt and releases pressure , from what I have gleaned from my interwebbing this happens before the bullet has left the barrel and therefore after a certain distance of bullet travel a longer barrel is actually a hinderance on speed , more so than a bolt gun.
Looking at the following chart I found for some interesting reading and am now considering 13 as a possible better length than 14 as the velocity seems to actually drop in some of the chart lines and in the firearm comparison bottom chart a ten inch barreled ruger is no different to an 18in 10/22 .

BBTI - Ballistics by the Inch :: .22 Results

Anyone have any real world experience with short barreled 22 down to say 12 inch in a semi type action or any input regarding their own short 22 ?