I don't know much about the calibers, but Im looking into varmit gun, I already have a .22. Something to shoot a lot of targets, but also maybe a coyote or something. Flat shooting and long range trajectory. Ive seen the .17 hmr, 220 swift, .223, .22-250 and some others. I need to learn more about the varmit rounds before I get one. Thanks

I've got a .223 and love it. .223 ammo is about the cheapest of any centerfire rifle, and it is the easiest to find. It also has the broadest choice of ammo selection. It shoots relatively flat out past 300 yards. The 22-250 and the 220 Swift shoot the same diameter bullet, just using a little more powder. They shoot faster and flatter, but can do a little more damage to the hides. 22-250 ammo can be found almost anywhere, but ammo for a 220 Swift can be hard to come by. Any of these rounds is deadly on varmints the size of coyotes or less. The .17 HMR is basically a .22 WMR necked down to a .17 caliber bullet. It won't have the range or the killing power of the larger centerfires. On small critters, its probably plenty. On coyotes, a .17 caliber bullet just isn't enough.

If you plan on shooting anything larger, like maybe deer, with the same rifle, you might consider a .243 or .25-06. These cartridges shoot very flat also, they just do it with more bullet. Relatively small bullets can be used for varmints, and larger ones can be used for medium sized game. The main downside is that these cartridges will damage the hides more than a .22 caliber centerfire. They also have a little more recoil (although it is still very manageable).

For shooting a lot of targets, and occasional chucks & coyotes, it's hard to beat a 223.
Ammo is relatively cheap too.
For long range varminting, go with the 22-250.
If you want a "dual purpose" varmint/big game cartridge, and good for long range use
on varmints, then go with a rifle in 243Win.

Another vote for the .223!!

A 22-250 is a good choice,but I prefer a .308win.I like it because I can go from popping ground hogs at 400 yards,to bear without a problem.Not in the same day,but yall know what I mean.Plus a .308 is a LONG range,FLAT shooting caliber.I can do 1000yard shots with one.You should try THAT some time.WHOLE LOTTA FUN!
Also you can get 308 ammo in 125 up to 180 grain.If you handload you can get down to 100 grains.Or so I've heared.

For suburbia I'd get a .221 Fireball, the Hornet brass is pretty fragile. I like to hold the noise down so the neighbors don't get upset. Loud noises equal danger to the great unwashed.

I would say .223. The Hornady factory loads have a 40gr V-Max traveling at 3800 fps which is not much slower than a .22-250. The .223 ammo is cheaper and brass for reloading is half the price of the .22-250.

I like my 6mm Rem.

If I were buying one I'd go with the .204 Ruger or 22-250.

223 is awfully practical, agreed.

.223 up to three hundreds and maybe a .243 after that.