WHOA!!!!
Before you try slugs you must know a couple of very very important things.
First: There are two very different types of slugs. Firing the wrong type of slug in your gun could be either damaging to your gun or else totally inaccurate.
)A. The first type is called a rifled slug. These are usually ok to use in a regular shotgun, except see below about chokes. Never use this type in a shotgun that has a special rifled barrel or choke insert. (Most shotguns do not. If the barrel is a rifled barrel, it will say so on it).
)B. The second type is called a sabot slug. This typed of slug is only to be used in shotguns that have a special rifled barrel specifically made for the use of sabot slugs. Or, a special sabot slug rifled choke insert can be bought for regular smoothbore shotguns that have removable choke cylinders. If you fire a sabot slug out of a regular smooth bore shotgun, it will aim wild. The sabot slug depends on the riflings in the special barrel to make it aim straight. Having said that, a sabot slug fired from the shotgun with the special rifled barrel designed for sabots is far more accurate than a regular rifled slug fired from a regular smoothbore shotgun. Never EVER fire a common "rifled" slug from a rifled sabot barrel. "rifled" slugs do NOT go in "rifled" barrels. They could seriously mess up the riflings on the special barrel and make it useless. (Usually, you will not have a shotgun with the special rifled barrel for sabot slugs unless you specifically chose it that way). If you don't know which typed of barrel you have, open the action of your shotgun to make sure it isn't loaded, and to let light in, and look down the barrel. If the interior walls of the shotgun are smooth with no design on it, you have a regular smoothbore shotgun. However, if you see spiral lines on the inside of the barrel (more or less like you would see on the inside of a rifle barrel, but not necessarily as pronounced), then you have the special rifled barrel for use with sabot slugs. You should never use ANY other shells with a sabot barrel other than the sabot slugs. If you have a Remington 870 smoothbore, you can buy a sabot slug barrel for your gun without having to purchase a whole new gun, and you will have a much more accurate firearm.
Secondly, as others have mentioned, there is the issue of the choke, which is at the end of the barrel. Keep in mind shotguns are primarily designed to use shotshells, which, for those of you in Rio Linda, are shotgun shells which shoot out a lot of little itty bitty pieces. That includes birdshot, which has tiny pieces, buckshot, which has big pieces, and anything in between. In the old days, and with some models today, you have to choose what choke you want when you buy the gun; it is fixed in there and not removeable. There are several different choke types available, and I may not know what all of them are called. The three most common, however, are full choke, modified choke, and improved cylinder. Now, from our discussion of the special sabot barrel above, the sabot barrel does not use a choke of any kind-- the end of the barrel is the same size inside as any other. But for the smoothbores, the choke at the end of the barrel serves to take that multi-pelled shot usually used in shotguns, and bunch it together when it comes flying out the end of the barrels, so that the itty bitty pieces tend to make a tighter pattern than they would otherwise. Of the three choke types I mentioned, a full choke is the most restrictive of the shot, and bunches it together the most. The modified choke is not nearly as restrictive as the full choke; it is a good all-rounder. The improved cylinder barely restricts shot at all-- it has the widest pattern of the three. When shooting regular shot shells with an improved cylinder, the pellets will range wide to the side in all directions as well as some going more or less straight ahead. Of those three, the improved cylinder is the best choke to have for firing slugs through. Still, I've heard many people say there's no real problem firing them through a modified choke. I've done it before with my 12-gage. I don't recommend shooting them from a full choke. That just seems a little dangerous to me. There is another choke even more restricted than a full choke, it is a special one for shooting turkeys. NEVER EVER shoot a slug from that one!
Now the really good news. You have a Remington 870. I don't know about the older ones, but to the best of my knowledge any sold within the last generation or so, have removable, interchangeable choke inserts in the end of the barrel! (my 12-gage is also a model 870, and I have at least 3 different chokes for it). These extra chokes are inexpensive to buy, compared with buying a whole new gun. If you want to run rifled slugs (that is to say, the regular slugs) through your gun, you should be able to buy an improved cylinder choke insert for it if it doesn't already have one.
Now about buckshot. Buckshot vs. hogs is ok, but I don't recommend it for a small gun like a 20 gage unless you are perched in a safe place where they can't "turn again, and rend you" as the Bible says. I did shoot a deer with a 20 gage with buckshot once, and although it did the job, the deer still ran quite a ways before it gave up. I counted seven holes from the one shot I fired. I shot at fifty yards, which is the outer limit for 20-gage buckshot. I aimed TWO FEET over the deer's back at that range, and my aim was excellent (if I do say so myself). Deer, however, are not anywhere near as agressive as hogs. You better be up on top of something or in something solid if you're gonna take pot-shots at a hog using buckshot.
last week a professional exterminator shot two sows a quarter mile away from my house. He sat on top of a utility shed and used a 12-gage with buckshot to kill them. He did a clean job. One sow weighed 180 lbs. or so, the other weighed about 250. They were the feral European wild boar that roam and terrorize all over most of the eastern half of the states.
To sum up, you can use your twenty gage equipped with the proper barrel/choke insert/ammunition arrangement, but I really recommend using a rifle instead. Don't stop at .30-30; I'd go at least .35 remington, .270 winchester, or .308 winchester, or bigger. A rifle lets you fire accurately from farther away, especially if equipped with a scope. Whatever gun you use, make sure you are practiced with it before you try to shoot hogs, and make sure you can aim quickly under pressure. Make sure you have your gun loaded with as many shells as it will hold and be fast on the reloading action. With buckshot I would aim for the ribcage. With a slug or rifle bullet, if you have time to aim well, line up a shot to go through the inner ear to the brain. Otherwise, aim for the ribcage.
Hogs are VERY dangerous animals. If you don't feel secure taking them on by yourself, by all means get help.
Hope this helped.
