RE: Light Weight Rifle
I read an article approx 2 years ago about barrel length and their test gun was a 7mm-08. The velocity drop from 24" to 20" was 60 FPS. You will probably loose 40 FPS at 22".
PS: This test ran the chrony at 24" and then cut and recrowned the barrel at 20" and ran the chrony again, so variance from barrel to barrel was eliminated. Many guys will get custom barrels that are 2" longer than standard and make significant gains in velocity, but many times the gain is due to reduced barrel friction and not the length. If you ask them, they attribute the increased velocity to the length of the barrel.