IMR 4350 vs H4350


July 6, 2008, 11:47 PM
I was told that these two were the same powder. I did some research and have discovered that they are not the same, but very close. That brings me to my question. Facts come from the Hodgdon data set. They list for Winchester, Hodgdon and IMR, I assume there is some vested collective interest between the three companies.

Bullet - 165g SIE SPBT 30cal (.308)
Load is for 30-06 Springfield
H4350 59gr, 2938fps @ 49,400 CUP
IMR4350 60gr compressed, 2934fps @ 57,600 PSI

What is the advantage of a compressed powder charge?
What is the advantage of extra air in the case?
Speed for the two charges is almost identical.
Is there a factor to convert CUP to PSI or vice versa? How do the two pressures compare to each other? If one is significantly lower than the other, does this translate to lower recoil?

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July 7, 2008, 12:11 AM
I find IMR and H to shoot the same. Technically there is a small difference between the two, because they are produced at different times and places, with two different companies maintaining the quality control. But when all is said and done, they shoot the same for me in 270 and 30-06. Your experience may differ, and I'd like to hear your results.

Compressed charge simply means that when you pour the powder in the case, the top of the powder will be below the base of your bullet, so the bullet will slightly compress the powder when you seat the bullet. It's no big deal and doesn't seem to affect performance.

Case fill: Many match competitors have found that a partially empty volume in the case leads to a very small inconsistency in burning, giving you a slight vertical string to your groups. I find that I get best accuracy a few percent below max load for most powders, which happens to fill the whole dang case anyway. So I don't really worry about case fill very much.

CUP is when they use a copper cylinder in a special chamber to test pressure in the lab. It's an old fashioned technique a hundred years old. The chamber is machined so the copper cylinder sits perpendicular to the cartridge case, and gets 'crushed' slightly upon discharge. The length of the crushed cylinder relates inversely to pressure. Contrary to what I've read on this Forum, industry engineers tell me there is no mathematical formula to convert CUP to PSI. For our purposes as sporting enthusiasts, you can think of them in a 1:1 ratio as far as perceived recoil.

July 7, 2008, 12:18 AM
The various "4350's" are similar, but aren't the same.

A cursory examination of H and IMR, reveal significant differences in their apperances. The H is a shorter cylinder and tan in color, whereas the IMR is longer and skinnier, and has a black shiney apperance.

There are also other similar burning rate powders such as RL19, H414, ect....

Personal experience is that the "H" generally produces higher velocities and poorer accuracy of the two (but not always!). It's also a tad bit slower and denser; hence the higher recommended powder charges as well as lower pressures at a given weight.

My preference depends on the application.

My Rem. M7 in 7mm-08 shoots wonderfully with IMR, but average with H and most any other powder.

However, my Weatherby Vangard in .257wbymag, much-much, prefers the H4350 over anything else for accuracy with a 100gr bullet. Velocity is about tops as well.

My .257Roberts (both!) prefer the IMR for accuracy, but the H clearly gives higher velocities with only a small accuracy penalty.

Go figure ! This holds true for most any particular rifle/caliber, hence why we have such a large and wonderful selection of propellants.......

re" cup vs. psi.

-apples vs. oranges; there is no real way to compare. The location of the electronic tranducers for determing psi are located in different locations in the chambers than that of the "copper crusher" used for the cup value, hence give different readings. The only cartridge for which I'm familar with where the two are considered interchangeable is the .45/70. Also remember that the copper crusher only gives the total average pressure, and may not accurately respond to the absolute peak pressure, nor the duration of the pressure curve.

However, remember too, that the data is only valid for the particular set of components in the test firearm, on the date of the tests, with the personnel conducting the test !!! Change even the lot#'s on the components and all bets are off !

July 7, 2008, 10:22 AM
I assume there is some vested collective interest between the three companies.The interest is that, Hodgdon now owns all three companies.

Well actually, they own IMR, and do the packaging and have exclusive distrubation rights for Winchester.


Mr White
July 7, 2008, 12:27 PM
Hodgdon 4350 is an 'Extreme' powder and will give consistent performance over wide ranges in temperature.
IMR 4350 isn't, and you'll get different performance n hot and cold conditions.

July 7, 2008, 12:49 PM
While the IMR and Hodgdon versions of 4350 are quite similar, the same cannot be said of IMR4831 and H4831. I like H4350 alot; have no love for H4831SC.


Harley Quinn
July 7, 2008, 02:14 PM
If you use the long drop method to filling the case many times a load will not be compressed (tighter filled) but not compressed against the bullet. If using the shorter method it will be touching and crushed some times, gravity will help, (it being a better, tighter load some feel).

Many use the powder that gives them a slight compressed or touching the bullet. The shorter, rounder fits in a case tighter as a rule, some will jiggle it to compress/tighten, more powder being able to use a slower powder, and not have as high of compression in chamber at time of discharge. The IMR, I was under the opinion was a slower burner. Maybe not?


July 7, 2008, 03:00 PM
Hodgdon 4350 is an 'Extreme' powder and will give consistent performance over wide ranges in temperature.
IMR 4350 isn't, and you'll get different performance n hot and cold conditions.

Precisely why I use Hodgden powders in more of my loads. IMR loads worked up in July generally will not shoot to the same POA in January. H4350 loads listed at the Hodgden site tend to be slightly less in grains than IMR4350 especially the max loads in the different calibers. That would indicate to me that IMR4350 is slightly slower than H4350 but the burn rate charts show the opposite. Another interesting note is that H414 and Win760 powders show exactly the same charges and pressures through the whole data chart for all cartridges using them. Hodgden probably has been making it for years. :what:


July 8, 2008, 09:20 PM
Grizz44 thanks for posting this thread. I have also been wondering if there is much difference in these powders. I worked up some 30-06 rounds with IMR4350 and they worked great. I worked up some 22-250 rounds and they too worked pretty good. I have purchased a pound of H4350 to give it a try just because of the extreme factor and hope it works just as well.

July 8, 2008, 11:19 PM
I just got 8 pounds of H4350, and used it in .243Win, 87 gr and 100 gr.
Quickload thinks that the loads with very long primer pocket life are ~62,000 psi.

.001" extractor groove growth the first shot is at 68,000 psi.

No growth ever is at 58,000 psi.

If I adjust the starting pressure to 7,500 psi for being jammed into the lands, then the predicted velocity matches the chrono measurements.

What does it all mean?
You know it is good canister powder when the velocity in Quickload matches the velocity in the chrono.
I like this powder.

July 9, 2008, 07:03 AM
IMR4350 60gr compressed, 2934fps @ 57,600 PSI
Work up using this powder. You may find that 57.0 gr is the real maximum in some guns depending on the brass used.

July 10, 2008, 03:32 AM
Like everyone has agreed on, H4350 and IMR4350 are not the same powders. According to the data on the Hodgdon load data site both will give you similar velocities but the H4350 will do so with a lot less pressure. I also found the rounds I make with H4350 are a little more accurate than those made with IMR4350. IMO any time you can achieve the same velocities and accuracy with less pressure it's a good thing. Why beat up your rifle and your shoulder needlessly?

July 10, 2008, 04:01 AM
Don't forget to add Accurate Arms' 4350 to the mix.

Harley Quinn
July 10, 2008, 03:03 PM
Some info on powders.


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