For a 12 ga. that will mostly be used for turkey but MIGHT be used a little bit multi-purpose. It is a Mossberg 835.

Do search for "Barrel Length" in this forum. There are several threads discussing that here. My opinion would be 26".

If you can change the choke its not much of an issue.

But if it is a fixed choke the longer the better.

I remember when I was a kid.
There weren't interchangeable chokes.

And at turkey shoots the shot guns with the longer barrels did better.

But if your gun has screw in chokes it doesn't really matter how long it is.

JMHO

For turkeys as short as you prefer will do. I currently have a 26" on my ithaca and if I were to order another for turkey it would probably be a 22" or 24". You do not lose velocity with shorter shotgun barrels like you do with rifle barrels. Of course these lengths are more suited for shooting from a rifle like position and not the best lengths for wing shooting. I hunt turkey, deer and squirrel with this shotgun so all my shooting is done rifle style. If I were to do wingshooting (dove, ducks, etc.) my choice would be a 28" or 30". The longer lengths do not give you extra range or velocity but act in the same way as a flywheel or balancer (the extra weight out front) to smooth out the swing on flying targets. In the golf with a gun games it is not uncommon to see 32" or longer. One thing that I do advise is for turkey guns (and for that matter any shotgun used like a rifle) to have the very best quality iron or fiber optic sights available.

I'm not a fan of short barrels unless it's for personal defense. Some will disagree with that, but I've owned and tested others and was never impressed. To each his own on short shotties. If it were me, I would lean to a 26 tube, which would be a good compromise for a dual purpose gun. There's ceratinly nothing wrong with a 28 or 30 either, but I wouldn't go shorter than 24 on any hunting shotgun.

Dally,

I have the 835 camo "Fly-Way" 28" non-ported.
Use it for Dove's, Duck's and Turkey's.

Mossberg also has......
The 835 "Turkey" 24" ported.
The 835 "Turkey Grand Slam" 20" non-ported.

Dally,
What mod 835 do you have? Mine is 28".

When you talk barrel length 22" to 28" with the chokes that they have now and the shotgun shells they have now, they all shoot well. But a 28" barrel has a better sight plain than a shorter barrel. If you are going to put a scope on it, I don't think it matters. I shoot 28" barrels on my guns.
Gselkhunter

If I was buying a new gun I would look for one in the 24" range...

I have a Rem 870 with a 26" barrel and it shoot awsome out to 45 yards. I put a 20" rifle sighted barrel on it and it does not shoot as good as the longer barrel. But I like a short barrel and I like rifle sights also. That is why I opted for the the shorter barrel