In general, but not always; a rifle will take more pressure than a pistol/revolver. So if it is safe in a handgun, it should be safe in a rifle. In the case of the 44mag there should be no difference in the maximum pressure between a handgun and a rifle. There is a max pressure standard for all 44 mag guns. A barrel that is 6" long and a barrel that is 20" long can see the same pressure, but get different velocities. Also different powders will work differently in longer barrels. A "slow" powder will have more velocity gain in a longer barrel, but not always. When power is ignited and starts to expand, is where most of the pressure builds. Once the bullet starts traveling a little distance down a barrel, the pressure drops. The longer barrel will let the expanding gases work on it for a longer period of time; thus getting more velocity. Slow powder will not burn as fast and gets a boost when traveling down a longer tube; in general. What does that all mean? just for an example; a given fast powder load in a handgun will give you 1000fps. The same load in a rifle will get you 1200fps. Now looking at a slower powder; say you get 1100 fps in a handgun and 1500 fps out of a rifle. You gain 200 fps with a fast powder and 400 fps with a slower powder. I think that some manuals give different loads for handguns and rifles so that the reloader will get a better idea how much velocity gain they will get out of the longer tube. In the case of the 45 Long Colt there is data difference between different loadings. There is the traditional pressure loads for older guns and a higher pressure loading for strong modern guns. This higher pressure load will out do a 44 mag, but the old traditional loading will poke along in comparison to a 44 mag. I am not advocating the higher pressure loads even though they are listed in some reloading manuals. I think you shoot them at your own risk. Even though a rifle will stand more pressure in 44 mag...Never - Never exceed manual recommended loads. You are asking for trouble. If you are not getting the velocity out of it you desire, then get a different gun with a higher velocity round, do not exceed max recommended pressures.