Contact Hogdon Powder Co. they are now in control of both varieties and will be able to provide with the correct answer to your question and not someones assumptions of which at times could be damaging to both you and your equipment.

J.Louis

IMR is #64 on the burn rate chart, and Hogdon is #65, so you should have no problem using the slower H4227 in place of IMR 4227.
Here's Hogdon's burn rate chart for future reference. It's sure helped me out a lot over the years!
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That's the first that I've heard of Hodgdon admitting it. I've had several discussion on the CastBoolit forum about this. I've always used the IMR and Dupont brand and have never wanted the H type. I bought two cans in this last year and then became suspicious of it because the can says made in AU. My assertion is that they dropped the real IMR4227 and replaced it with H4227 (probably to make more profit) and then dropped the H4227 name because the IMR name is more used and respected. Fine if they told people but, it seems to be under the table. I haven't test one against the other but, when I want IMR4227, I don't want H4227. I've since bought 7lb from gun shows and a friend to have what I spend my money for.

Frank

Joe_S you might want to consider a powder change as there are allot better powders out there other than 4227 for your 38-55. Alliant 300MP is one of them and if you would like to give it a try send me an e-mail at johnlouis123@att.net and I will pass on my test results and load data for your review. 

J.Louis

Gunny we like Martini's a lot around here.  I had a KHornet T/C Contender Carbine great shooter with 4227.

If you work up loads with whatever 4227 you have they ought to be fine. Only thing to watch is changing to one of the other 4227's  Back off just a bit then work back up.  Treat it like two lots of the same thing, which is what it is.

Boats