No, I don't think that is correct, unless you might be shooting an early 19th century, or earlier ORIGINAL rifle made of iron, not steel. Then I would be concerned about chamber pressures.
Small caliber rifles are going to produce the greatest rise in chamber pressure using FFFg. However, if you are using a 50 caliber or larger bore rifle with a steel barrel, go ahead and use FFFg powder. With large bores, .58, .62, .69, .75, you don't need a lot of powder to kill game out to 100 yards or so, which represents about as far as most shooters can use iron sights accurately, and about as far as round balls can be shot at Point Blank ranges( ie. hitting no more than 3 inches higher or lower than POA). 70 grains is usually all that is needed in these big calibers. Its the weight of the ball that controls the depth of penetration, and not velocity, after about 50 yards. Increasing velocity is done to try to flatten the trajectory of the ball going down range. Again, at 100 yds, the trajectory is just not that much using a reasonable charge of powder.
Whatever caliber you choose to use, do some penetration testing. The medium you use is not as important as using some other gun you know will kill the game you are hunting to shoot into the medium to establish a comparison benchmark. I made a penetration box using 1 inch pine boards, spaced 1 inch apart. I learned a lot about my gun, and other guns I own, shooting both round balls, and bullets, until the boards were falling apart.
