220Swift your question and Bigbulls answer just about sums up a lot of the debates on why people don't think their rifles won't shoot and are not accurate. First people go out and just buy a rifle. They didn't put any thought into what the intended use was for or what grain of bullet they wanted to shoot through it or the velocity at which they wanted that particular bullet to travel at. It causes a huge dilemma for the rifle owner to figure out. In today's information highway it shouldn't be such a big deal to have the knowledge before you actually purchase a rifle.
About 15 years ago I learned this the hard way. I bought a 22-250 with a 1-14 twist. I went straight to 60gr bullets and with a brand new rifle I was only getting 2 1/4" groups man I was upset. Then I tried some factory 55 gr loads and got some modest 1 1/2" size groups. I was besides myself thinking .223 caliber ought to be dang near holes in holes at 100 yards. Standing in Wal-mart I saw these 45gr Winchesters 4000 fps and I could get 40 rounds for $18.00 so I thought what the heck I'll try them. And they shot 3/4" groups everytime. Then a little light started going off in my head what if this rifle likes smaller grain bullets. So back to the reloading bench I went. And today the same rifle shoots under 1/2" groups every time at 100yds using 52gr bullets. I was upset, had no faith in the rifle even though it was one of my favorite models and I just about sold it. AND THAT ALL BOILED DOWN TO MY LACK OF KNOWLEDGE AT THE TIME. I paid a little for my education but some are paying a lot more than I did for it.
Rates of twists and optimal bullet weights for those twists is a good topic and a great starting place when your thinking about purchasing a new rifle for a particular usage. If your going to shoot 75 gr Amax's out of a .223 you better get the barrel that fits that bullet.