I'm not much into scatter guns. But I bought an old savage 12 gauge. 18 in barrel, 2 3/4 to 3inch shells and it's a pump. Looks like an old trench or riot gun. It holds 5 I believe. I never shot it yet but my sons have. Mt questions are, my bud told me for home defense get 00 buck. Ok I am lost when it comes to buying shells. Bought some cheapies not long ago. Bird shot I was told it was from a friend. Another friend said to buy 8 or 7.5 but I'm probably wrong. Gonna be using shotgun for like rabbits, rockchucks, small game. And to mess around and shoot stuff. So which would you guys recommend? The bird shot I bought wouldn't kill a rock chuck at 20-25 yards. Or is the shotgun just made for home defense? I reload for rifles but I'm lost. Which brand you prefer to? Thanks a bunch.

For rabbits, squirrels, ground hogs closeish, pigeons, work for doves, I’d go 7 1/2 shot.

I like 1 ounce loads at 1290 to 1330 fps

Some will complain, but I do not have a problem with 1 1/4 load of 7 1/2.

Got how defense, how close are you to other houses. I killed feral dogs off a deer w 2 ounce No 4 bird shot (turkey load). Across a bed room. I have no need for buck.

No 5 shot makes great work in ground hogs.

At in house distances a charge of any size shot will be virtually a single slug so the shot size will make no difference to lethality or penetration through house walls i.e. there will be grave danger to assailants with a good hit and similar danger to innocents inside a house with a miss or even a pass through from an assailant hit. So in reality a shotgun is not the ideal home defense weapon and even with a short barrel they are still unwieldy in many situations, a two hand hold required for pump operation especially.

As for small game I have had great success over the years on duck, shelduck, geese, swan and other birds with a fast reload (1325fps) of 32gm #7 lead shot. Now with steel shot mandated for waterfowl I use factory 32gm or 34gm #3 or #4 shot.

--bird shot (7 1/2, 8, 9) is good for skeet, trap, pigeons, dove, rabbits (7.5).
--lead 6's were good for ducks and pheasants. Steel shot (req'd for waterfowl) isn't as effective at the same size.
--2's and 4's are good for geese and ducks, where the shot has to carry further. 4's would work on badguys, or as stated above, very close anything works.
--Buckshot is good for deer or similar large animals or bad guys. "00" double-ought is the most available and poplar, though some folks think "0000" or other sizes are better.
--Slugs are good for big game or bad guys.

In the early 1970s I knew a friend of my father's called "Tiger" Chapman. He and my father fished together. "Tiger" was called such as he'd shot, once, a tiger in India during his service there. Impressionable from having read Corbett I asked Mr Chapman, as he was to me what he'd used.

A 12 bore, side by side, was his reply. I imagined all sorts of exotic paradox bullets, colindian bullets, Kynoch "lethal ball" and etc.. So I asked what he'd used in it. "Number 6...it holds together remarkably well at close range" was the answer. The number six being English #6 and likely for the time 1 1/16 ounce or 1 1/8 ounce of the stuff. The equivalent of English #6 at close range would effectively be a fist sized mass of lead shot.

Many. many, many years later now in my twenties I met one of the UK's forensic ballistic experts and the conversation turned to buckshot. His experience, he said, that at short range on a human target, it made no difference in lethality. That 1 1/8 ounces of English #6 at five or ten yards would be as lethal as English LG (five balls of .36 diameter).

But there was one caveat. At ten yards five LG buckshot if they didn't kill would be easily removed and the wound heal. Whereas 1 1/8 ounce of English #6 at ten yards would create a wound that simply could never be repaired as there would be nothing to stitch one part of it to another part of it. It'd be all "holes". If it was gut shot you'd be using a colostomy bag for the rest of your life.

So you takes your choice.

But I bought an old savage 12 gauge. 18 in barrel, 2 3/4 to 3inch shells and it's a pump

You have a decent shotgun with most likely a cylinder choke.

AS a shotgun instructor. Getting or giving advice in a paragraph or two is really hard

I would suggest that you find someone local that knows shotguns to help you out.

A local gun club would be a a good starting point.

It is more of a defensive shotgun then a hunting gun. But it can be used for that purpose just not as effectively. With the cly choke really limits. The distance for hunting purposes.

For self-defense hard to beat 00 buck.

Buy several kinds of shell get some large pieces of cardboard. Go to the range and test them out.

Since you said you are new… very simplified version…

Shotguns, like anything else kill via projectile placement and penetration.

If your gun isn’t killing rockchucks at 20 yards look at those two issues. Larger pellets will give more penetration, but the pattern will be thinner- so less likely proper placement of the pellet into a lethal place.

Traditionally this was solved by using more shot (target loads are anywhere from 7/8 Oz of shot through 1 1/8 Oz of rather fine shot)

Game loads are roughly 1 1/8- 1 1/4 Oz.

Magnum loads (again assuming 12 ga 2.75” shells) are 1 1/4- 1 5/8 Oz of shot. Target loads are rather variable in velocity- for game work you don’t want reduced velocity, aka managed recoil or LE loads.

Another way to deal with pattern density is choke boring the gun. Today, they tend to come with choke tubes that allow you to choose what constriction you want- the tighter, the more dense the pattern. You are trying to get a happy medium of dense enough to kill at the distance involved- thus the comment on testing patterns. Different loads can pattern very differently- I cannot get cheap Estate shells to pattern for sour owl jowls in my high end beretta sporting clays gun- but they do pattern ok in my benelli duck gun for shorter range use- brand, type of shell, and individual gun all are independent variables here.

Fine shot looses velocity quickly. While #9 shot (about as fine as you can get in commercial lead ammo) will have very dense patterns because there are more pellets, it rather rapidly becomes ineffective due to velocity loss, and will not even break clays reliably after 30-35 yards (some say even shorter distances).

Compare that to 0000 buckshot which will (if you hit) penetrate a person past 100 yards.

A rockchuck is a relatively dense animal, so while 7 1/2 is good for smaller birds and rabbits, it’s not that good on varmints past conversation distance. If you want it dead on the spot, go for #6 to #4 shot at 20-35 yards… but be aware that you will likely tear up whatever is behind it with that heavy of shot.

A thicker pattern can make up somewhat for penetration, but only somewhat. Shoot a deer at 25 yards with #8 target shot in an extra full Turkey choke gun, it may die from infection, but it’s not going down fast. Shoot a duck (illegal with lead but for purposes of discussion) at the same distance, and it will fall, but still likely be moving on the ground. At 10 yards, assuming a proper hit, the deer dies and the duck is hamburger.

Usually game loads come with a blurb on the box about what they are intended for.

8-7 1/2 is small birds like dove or quail and as these are usually short range propositions they tend to have less shot in them.

7 1/2 to 6 is typically rabbits and grouse. I also stay here for pigeons (varmint variety)

6-4 is for bigger upland game- grouse sometimes, but pheasants typically.

2 is big birds or close bigger varmints. Some folks use this on Turkey, but usually you are head shooting Turkey and use smaller shot.

BB is longer big varmints like coyotes.

In the old days for very high geese some would use #4 Buck (aka FF in steel parlance)

Buck ranges from #4 buckshot at the finest (I think it’s .24 caliber) to #1 Buck, then you go to the O sizes, where it reverses and the more O’s, the bigger it is. OO Buck is roughly .36 caliber roundballs.

Then you get into slugs.

So shotgun ammo is very use dependent and specifics depend on your gun.

If you start getting into nontoxic shot, the above is all different again.

Steel is about 70% as dense as lead, and thus you need both bigger pellets and more velocity for it to be terminally effective.

Bismuth is about 85% as dense and is roughly the same as lead, but about 5x more expensive.

Then there are the tungsten derivatives.

These range from alloys that are roughly identical to lead, to varying degrees more dense, to pure tungsten (tungsten super shot) which you can get away with very fine shot in relatively small amounts at extremely long ranges, but it’s extremely expensive. Some are willing to pay for the effectiveness it gives, but at $5-10 per shell, it’s a bit much to me.

Hope that makes some sense.