its not the 14/1000ths of a inch that makes it it is the extra 20gr in bullet weight.

Old fashioned here. I wouldn't use a varmint cartridge on targets over 100 pounds, although poachers drop them with much less. The 257 is heavier and with more frontal area.One of my coworkers loaned his 257 Ruger to his wife. She never gave it back after the first season.

.243 every time.
If you want to use a long action case with mild recoil and significant killing power, try the 6.5x55.

Get the 257...you may not have 50 different factory loads to choose from but you only need one. If I remember correctly, either Federal or Remingtonsellsa +P loading for the 257. When it comes to lightweight rounds, Ilike the fact that you can shoot a bullet that is 20% heavier with a slightly larger cross section. Currently Iprefer a 7mm-08 to either a Bob or 243but that is a whole different topic

.243 all the way. it is one of the best cartridges for young hunters ever made. average shots for deer hunting are 100 yards or less.

The .243 is a suberb cartridge, and is a little better than the .257 Roberts for varmint shooting. The .257 Roberts is a superb cartridge, which will work for varmint shooting, and is better than the .243 for deer. For deer mainly, the 6.5X55mm, 6.5X57mm, or the .260 Remington is better than either the .243 or .257......

True, you only need one good factory load for it. But if you don't reload, then the more factory loads available the better your odds of finding an accurate load for a particular rifle.I knowI have sometimes gone through 4 or 5 different factory offerings before finding one thatwas accurate from a particular rifle.

How do those few extra grains help, when it doesn't hit as hard? A couple of guys have mentioned the greater frontal area of the .257. Isn't that where those 14/1000th's come into play? Doesn't bullet speed at impact have an effect on the amount that the bullet expands? At nearly 500 fps faster at 200 yards, might not that .243 bullet expand to a greater diameter than the slower moving Bob?

Remington has one load for the Roberts. I chose the most common deer load for the .243 as a comparison:

Someone mentioned +P loads for the Roberts. Hornady makes one, but it makes one for the .243 as well. As someone said early on, the .243 Win. made the Roberts obsolete...

edit: Winchester also makes a .257 +P, and I've added its ballistics. Even the +P load doesn't compete with the .243...

The .243 Win. isn't just a "varmint cartridge". Most certainly not when being compared to the Roberts.

If you only shoot factory I kinda lean to the 243, but if you handload its a diff ball game. I get over 3100fps with a 100gr bullet and dang near 3000 with a 115gr out of a 22" barrel in the 257. Most 243 100gr factory loads are getting around 2900 in standard barrels with some being a lot slower. There are some good bob factory loads as well, like the Hornady light mag and other +p loads. Me for one I just love the case in the 6mm,257 and 7x57. And you can not go wrong with the 6.5x55,260, 7x57 or 7mm08.

I have taken lots of deer with the 243, 250 Savage and 257R. I don't like the 100 grain bullet in the 243 because its SD is higher than I like for deer. However the 100 grain 257 bullet is about perfect IMO. I get 3100 fps with the Barnes X bullet in the Roberts with the 700Remington rifle and 3050 from the 250 Savage.