Until recently they were different companys.
Truly, I never understood the similarity in numbering, and wish Hodgdon had stayed away from IMR.
I use both, but IMR is better for some cartridges, it's more consistant lot-to-lot, and as temp stable(if not more so) than Hodgdon, despite the hype.
I don't like them fiddling with good ole reliable IMR.
Anyway, do not assume they are the same because of the number designations.
Hmmmm - these two powders are always found together on the burn rate chart for a reason. They have very similar burn rate characteristics. In my experience they vary very little in actual use. A load could be tailored with either one. That's not to say they are the same or directly interchangeable, just very similar in their use.
Just my 2 cents from using both powders in a few cartridges.
This is an exmple of my basis for significant differences:
On a 6.5WSSM running 47.4gr IMR 4350, I get 3040fps with Lapua 139s..
Quickload 'what-ifs' for 55Kpsi(my pressure) AND </=100% case fill, all else equal:
IMR4350 comes right to the top at 98%fill and 3044fps.
Interesting and related in order below are:
Hodgdon H380 95%fill and 3033fps (needing same 47.4gr)
IMR 4831 100%fill and 2988fps
Hodgdon H414 90%fill and 2988fps
Hodgdon H4350 100%fill and 2966 (needing 48.6gr)
This tells me that H380 is closer to IMR4350 than H4350.
There were 15 other powders between these. And, in this case, any listed could be used safely. They just can't be assumed as same, and for sure one will best the others in your gun.
As has already been pointed out here, they are two entirely different powders and should not be interchanged. As to which is best suited to a measure, right now that'd be H4831SC. The SC designation indicates a shorter cut kernal, but the powder remains identical to (and interchangeable with) the original H4831. I'd suspect that IMR will introduce an SC version as well, but just haven't seen it yet.
Hate to break this to all, but they're pretty random, and ther result of marketing decisions. May vary a bit from company to company, but that's the case for most that I'm familiar with. Hodgdon's "H380" came from Bruce Hodgdon's favorite load with that powder (GI surplus at that time), 38.0 grains in his 22-250. I understand that IMR3031 came from its ability in replacing cordite grain for grain in charge weight in the British service cartridge; hence we have IMR "303"1, or IMR 3031. There's more, but you get the idea.
Pretty convoluted, for the most part, and a good reason not to try to read too much into a designation.
With H 4831sc you might not get the highest speeds, but you will get your best accuracy and temperature consistency. My 300 WM shot to exactly the same aiming point at temperatures from 75 *F to 0*F with H 4831sc and F210.
H 4831 is preferred by the bench rest crowd.
IMR 4831 may get you higher speeds but I don't know what else.
I guess it depends. are you looking for MOA or MOE ? (Min. of Elk )
They're both kind of a pain to load because of the large grain size. Ball powder like Magnum sure goes through the powder measure more accurately. lightbulb