SKS barrel is 20”. I’ve shot at clay at 400 plus yards with an SKS and had the bullet penetrate about 1/2 its length.
You can get a little more out of it with a Yugo 22” barrel. I did... :)
https://www.apexgunparts.com/sks-barrel-yugoslavian-model-59-66-7-62x39-nos.html
https://www.gunbroker.com/item/898784797
And contrary to popular belief, embedding an SKS actually does work and greatly improve accuracy.