Alright experts, my wife is wanting to upgrade from her youth model 20 gauge to a compact 12 gauge. The bulk of the hunting will be for ducks. I've found a few compact 12 gauges with the same length of pull as her youth gun, but the question is would she be losing any benefits by having a 24" barrel vs a 26" such as effective range and pattern?

None, other than weight & balance, she will probably never notice the change.

And just to make sure I understand correctly what I've already researched, I should see the exact same pattern out of either size barrel at the same distance correct? As well as the same velocity?

I’ve heard some women have problems going from a long barrel to a short barrel. Some will use a short barrel and keep a long one in reserve. It’s all about personal preference.

Just kidding, but it is about personal preference. I can shoot better with a longer barrel shotgun. That’s what I use for dove and duck. If I’m quail hunting I prefer a shorter lighter gun if I’m carrying it all day. Buy her what she feels the most comfortable with. If she feels better with a longer barrel, buy that gun and have a smith cut it down to whatever length of pull she needs. It’ll cost you about $100 with a good recoil pad.

Shorter barrels are a little closer to the ears.

Yes, the barrel length difference is mute, the same as a 26" vs 28" barrel. Chokes can modify the pattern depending on the distance to target

If you think you need the extra few inches you can always add an extended choke tube. I put a Pure Gold extended choke tube on my gun and I thought it really helped, especially on long cripples.

The extra weight will help with the recoil. I've found that for me, I shoot a longer barrel shotgun better due to the extended sight plane.

Extra length and weight will help with sight plain and keeping swing in motion.
And a 28” will shot 2” further than a 26”.

Shotgun shells are tested with 30" barrels. You will also gain or lose 15fps for every inch you go on either side of that 30". So if a shell stated they shoot at 1250 fps with a 28" barrel it will shoot roughly 30fps less (1220fps) and with a 32" barrell it will shoot 30fps faster (1280fps)

Shorter barrels are normally controlled better by small statued people. Longer barrels are normally handled better by larger statues people.

My personal opinion is to find her a gun that fits her LOP and drop at heel and that feels good to her in her hands that she can mount and shoot effortlessly

choke is the key, not length.

Complete myth, length has little to do with velocity, overbored barrels of the same length are significantly faster velocity wise. Back bore, tri-bore, over-bored barrels disprove this myth repeatedly. Mr. Baker sends his regards.

30" is the standard because the majority of proof barrels are 30" and longer, it's to obtain pressure/SAAMI data not just velocity.

Franchi Affinity 3 compact 12 with the 26" barrel. My wife is tiny and she can swing that gun easily. Lightweight, Benelli's proven inertia drive system in it, and just a great all round gun. If you're worried about barrel length, go for an extended choke.