My 15 year old daughter will be hunting Spring time gobblers this coming spring. She will be shooting a pump 20 gauge shotgun. What is a good size shot to use and what brand shotgun shells will bring down a gobbler? How close to you recommend the turkey needs to be for a quick kill?

No longer than 20 yd shots. Of course use full choke if your gun has one. 3" #4 lead, but you already knew that.

Do you have a semi auto 12 gauge?

The pump 20 gauges tend to kick like a little mule.

Any high brass 20 gauge with #6 shot and full choke should get the job done inside 30 yards.

With a good turkey choke and some Federal TSS shot, you're getting very close to 12 gauge performance from a 20 gauge.

Be sure and practice with her. Start with some light loads and build up to heavier loads. Biggest issue I've had with kids is not getting their head down and firm cheek weld on the stock.

First off congrats on hunting with your daughter.
I use the same 3" 1 1/4 ounce copper plated lead #5 Federal WingShok @ 1300fps I use for pheasant out of my 20. You will need to pattern a few different shells to see what her pump likes best. The patterns her 20 throws will dictate what the effective range is. That is the only way to know. Harder shot usually patterns better as does buffered shot. In my back bored Citori it patterns best with a Mod choke and is good to 45 yards. What her shotgun prefers and how
It patterns will likely vary. Depending on her skill level, if she needs to practice, after you find the load, let her practice with low brass dove loads. Save the magnums for turkeys. More than likely, on a bird, she will barely notice the recoil.
Best wishes to you and your daughter.

Heavy shot sells a turkey load lower recoil that patterns well from my 20s and is deadly from them to 40 yards or a little more.

They are even more expensive but the Federal TSS loads will recoil a bit more but the #9 shot is good to 50 yards or more and usually patterns very well. With this stuff would have her shoot before the turkey is inside 25 yards becausethe pattern can be real small

3" federal heavyweight #6s

pattern the gun and let it tell you the distance. I killed my slam with my 20ga, and now I hunt with a 28ga. My 20ga 870 with TSS hand loads will kill further than you need to be shooting at one with a shotgun. I would start with either TSS or Hevi shot in the gun.

Good luck finding them. Heavyweight was replaced with TSS last year.

Google is your friend! Still a fair amount out there on the internet and in stores. I stocked up with about 10 boxes!

Cool. I sold all mine last year when I started rolling my own TSS shells. I can remember quite a few having trouble finding it still in stores on another forum. Still a very good shell. Hits like Thor's hammer.

Is this what you guys are referring to?
https://www.luckygunner.com/20-gauge-3-1-1-2-oz-9-shot-federal-heavyweight-tss-5-rounds

Yes, that's the TSS.

Can anyone tell me, is it worth it ???

I think it is for the pattern density alone.

My turkey gun is an el cheapo Stevens break open 20 guage with full choke. I use Remington Nitro Turkey no 5 shot. within 30 yards, usually DRT.

What shot size would you recommend ????

9's. They have the same energy as lead 6's. They also retain there energy longer being more dense and won't deform like lead. Most will pass right through.

I like a duplex load if you can find one and copper plated , hevi shot or tungsten.
Don't let her lean that shooting shoulder against the tree trunk when she takes the shot.

I reload my own TSS 1 5/8oz of #9 Shot. The pattern I get out of my gun is ridiculous. It is far superior to most 12 gauge lead loads. I will never go back to toting a 12 gauge again. In a 10in circle with reloads I average 310-340 in the ten with over 220-240 in the 20. Not too shabby for a little 20 gauge.

The 9s actually have the same energy at 40 yds as #5 lead.

I don't advocate shooting turkeys any longer than 40 yds, but with reloading TSS your 20 gauge is a no $hit 60+ yd gun if need be. A buddy of mine killed one last year in nebraska at a ranged 75 yds with the load I mentioned earlier. Bird was farther than he originally thought due to rolling hills. He and I both thought the bird was around 50 yds.

20 is my go to for turkeys. Hevi Shot #6. Shooting those out of my 870 with a comp-n-choke, have killed several birds at 60+

If it were me and I wasn't reloading I would get loads from APEX or either the Federal Heavweight Magnum #9 TSS.