I had a 24" on my Affinity 20 and now a 26" on my M2. Never noticed any difference. In my experience both 12s and 20s, I got better pattern performance out of 24" plus barrels. Results for others may vary. Barrel length never handicapped me in the woods and I like the muzzle blast a bit further away from my ears. Sumtoy chokes are short so I don't have an extra 2" screwed in the end. Think you will be happy with either length. With the M2 20, I think 24 is as short as you can go.